On a 1-5 star rating:

5 stars for the DAC/Preamp (considering its price point)
4 stars for the Controller App. (works well with a few annoyances)
3 stars for the documentation.
2 stars for no WiFi.
1 star for its native file handling capability BUT with a freeware software solution it becomes 5 stars (see below).

This review is more focused on providing a review of the functionality of the DAC of those things that may not be obvious from the documentation. To keep this as brief as possible I am intentionally not restating what can be found in the product documentation since you can read this for yourself.

While I am calling this a review, I am purposely not saying much regarding sound quality which is so subjective and system / room dependent. But I will say I am very happy with the sound quality of this DAC. I upgraded from a Bluesound Node 2 and realized significant and noticeable improvement in sound quality plus higher resolution and DSD.

The controller app itself is pretty good but a lot of its functionality is not documented so you also have to figure it out on your own. Once you do you will realize it’s pretty good. It just takes some time to get used to. There are a few functional annoyances but that may just be because I am used to using the BluOS app.

STREAMING SERVICES work very well. I tried it with both Tidal HiFi and QoBuz HiRez. The MQA decoding of Tidal sounded excellent, so good I am not renewing my QoBuz.

REQUIRES A HARD WIRED ETHERNET CONNECTION because the controller app will not work unless the DAC is directly connected to your router via Ethernet. You should not purchase the NT-505 unless you have a hard wired Ethernet connection available. The DAC does have both coax and Toslink inputs so one could use an external streamer connected to the digital input on the DAC but then you would have to use the streamer’s controller app and none of the other functions of the NT-505. That really wouldn’t make sense.

MUSIC FILES ON A SERVER OR NAS: The native file handling capabilities of the NT-505 are awful if you have a large number of music files. It is slow to load and every time you turn on the DAC or your controller app it seems to take forever to re-load. I was ready to return this DAC until I noticed a single line in the documentations were TEAC recommends third party free ware called MinimServer to access and manage music files instead of their own software. You MUST use MinimServer if you have any significant amount of music files in your library.   MinimServer is very fast to load large amount of music files and more importantly maintains the index of music files in the server’s memory even when the DAC is off so it doesn’t have to rebuild the index every time you turn on the DAC. MinimServer performs very well with 1T of music files that I have stored on a remote PC. If you have a NAS compatible with MinimServer you can install MinimServer on the NAS and then use another free software called MinimWatch on your PC to configure and control MinimServer. MinimServer and MinimWatch are both very well documented and a Google search will get you all you need to know.

MUSIC FILES ON LOCAL USB DRIVE: The local USB port on the front of the DAC is intended for USB thumb drives but with this configuration you can’t use MinimServer and are limited to using the DAC’s native file management with the limitation described above. But with a smaller number of files this isn’t that much of an issue. I tested it with a connected HD with about 200 GB of music files and it did ok but when I tried loading more the DAC choked and froze.

PLAYING MUSIC FROM A COMPUTER: There is a USB type A-B connection on the rear to connect a computer directly to the DAC but I have not tested it since this DAC can play all high rez and DSD files from the a remote server or NAS.

I am not going to plug any source for purchases except to say that I bought the DAC from a large online seller that offers a 60 day return for any reason with full refund or credit for something else. That is more than enough time to fully evaluate this DAC.

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The Teac HR Streamer app is in fact a variant of the Lumin app which also works with the Teac.  Most of the missing documentation you are looking for can be found on the Lumin site.  I switched to using the Lumin app instead of the Teac one as it is updated more often.  
Page 13 of NT-505 manual, "You can use the upconversion function with all input sources."
A far as where I bought it, I bought it from Crutchfield.com because of their return timeline.

Thanks for that. I downloaded the Lumin app and it looks like the exact same app! I see it has a lot of instructions on its use on the Lumin site.
Thanks for sharing all the info with us. Can you play mp3 music files on this DAC (either via a flash USB drive type-A or via Bluetooth from your smartphone)?
Yes, it plays mp3 files. I did a test and played some mp3 files from both a thumb drive connected to the front USB and from my PC using MinimServ. I have not played any music via Bluetooth.
I’m interested in this unit. Have you compared it sonically to any stand-alone DACs in that price range?
I have not made comparisons to other stand-alone DACs in this price range. I will say that this DAC does not have a sonic signature. It gets out of the way. So if you are looking for a DAC that "adds" something this may not be it. The only other "dacs" I own are the Node2, Oppo 203 and a Musical Paradise tube DAC. I prefer the TEAC over all three. So much so that I am now also using it as my pre-amp in front of two CARY 805AE mono amps.
Musical Paradise tube DAC was on my short list...
looks like it will probably be the TEAC unit with the NAD C658 second place
SMSL says their AKM Veritas 4497 chipped units will have MQA in the future
ah, to save a thousand bucks...

And just to be clear, the Musical Paradise DAC is a wonderful sounding DAC. I do recommend it if you don’t already have a tube system. It is just that in my tube system I liked the TEAC better. I will likely be using the MP DAC in my SS second system which I listen to most of the time. Right now I am using a Node 2 as the DAC and using the MP DAC  with the Node 2 is a noticeable improvement.
Anyone using the 505 as a Roon endpoint?

Mine just arrived and I’m using it with Roon. The unit sounds absolutely fantastic so far. Roon works perfectly with it. You’ll need to give it the most recent firmware. 

I started this thread five months ago and after using the NT-505 feel compelled to submit an update.

1. I am still thrilled with this product. In my prior review did not emphasis what a great PREAMP this DAC is because I was using it with a preamp and was just using it as a DAC. I am now using it in place of a tube preamp that costs new more than twice the NT-505. The description of this product should include the word "Preamp" somewhere because it is a Preamp/DAC.

2. I moved the NT-505 to an area of my home without an Ethernet connection. Not a problem for me because I am using my Bluesound Node 2 as the wifi streamer and connected the NT-505 to the digital output from the Node 2 which bypasses the Node 2's DAC function and uses the NT-505's DAC and MQA decoding functions. So no degradation of sound with the Node 2 as the streamer only plus I get to use the BluOS app controller which personally I like much better than the Lumin Controller App. These comments would apply to the newer Node 2i as well and likely any other standalone streamer if a buyer wanted to use the NT-505 somewhere without a hard Ethernet connection. Now I consider the lack of built in wifi a plus rather than a negative.
I try to use Minimserver to scan my music library on my Dell PC accessible from the Nt-505 but could not make it work.I installed Minimsever on my desktop PC.I installed the Lumin app on my iphone, but this app does not see my music library on SSD.Do you have any suggestions? 
Get a copy of the Minimserver User Guide. It explains how to configure it.
After you install the server and the desktop icon is green, click on the small icon in the tool bar. Under properties you define which drive your music is on. You should then be able to activate Minimserve from the Lumin app. But download a copy of the User Guide first.
   Node 2i as well and likely any other standalone streamer if a buyer wanted to use the NT-505 somewhere without a hard Ethernet connection.

Now since you had the node2 hanging around, that is one thing, but at $550 it is just about the most expensive solution to needing a wired connection that I can think of.  Since you will definitely need to install this thing near an electrical outlet or six (depending on related equipment), one of those units that uses your home's AC wires as an ethernet cable should work just fine.  They usually have at least one ethernet port as well as wifi.   Some even have pass-thru AC so they don't actually use up a receptacle.  $50 or less.  Note:  Even the most hi-res recordings do not require huge bandwidth, so you don't need the fastest unit out there if its mission in life is to connect to your streamer.
I'm using Serviio as my music server.  My NT-505 had no problem finding and indexing all the music on my shared drive on my network.  Serviio is free.
That is a good suggestion. I Googled Ethernet over home AC line and saw a number of low priced options out there. One reason I prefer my Node2 as a streamer is I actually like the BlueOS app interface more than the Lumin app. I am also now subscribing to Amazon Music HD and have not found a way to stream AM HD using the Lumin app. The BlueOS app streams AM HD fine.
I also have the NT-505 and love the unit although I had the rear Network plug/connection fail and had to send the unit back for warranty repair work. The TEAC was fixed, no cost to me, and now works as good as new. I did not have the patience for the TEAC app, also thought it was a real pain having to reload / look for all my music files each time I started the TEAC up. I have over 4TB of various types of files from the lowly mp3 to FLAK to native DSD files. The TEAC app was also slow to page through all my files so my solution was Roon. Roon works amazingly well with the TEAC and through Roon I access Tidal, which also works flawlessly and sounds great. One reason I chose Tidal was for the MQA experience, which the TEAC unfolds. I have mixed feeling about MQA, but since the TEAC will unfold this type of file and many do sound amazing, why not subscribe to a streaming app that has it available and therefore have one more file type I can listen to. For the price, which falls under $2K it is a steal. I think it does have its own voicing and that is one that makes digital a little bit smoother. Maybe it rolls the top frequencies a little or filters off some of the digital glare, but what ever it does it makes the music so enjoyable. I use the TEAC with a tube preamplifier and tube amplifiers and this in my opinion is a great match up, however I believe it would sound fantastic in a solid state system also. With solid state it might not be as "smooth" sounding I don't know haven't tried, but I do recommend the TEAC as a great Streamer/DAC/Preamplifier/Headphone Amp.
what tube preamplifier are you using with the NT505?
Have any NT-505 owners invested in the Teac 10MHz clock unit and added it to the NT-505?  Was the performance improvement subtle or dramatic? 

I recall reading a review before purchasing my 505 that said the improvement was marginal or words to that effect.
I am still enjoying my NT-505 and am happy I purchased it but one thing I would like to clarify is that it is not really a preamp because it has no analogue inputs. It is a digital streamer DAC with a volume control and multiple digital inputs.

As I mentioned above I was using MinimServer which works well but then I acquired over 10T of digitized music so started a subscription to ROON and could not be happier. ROON works very will with the NT-505 which is a ROON endpoint and if you also have a Tidal or Qobuz subscription it is even more impressive.
I have two main systems, one solid state and the other tube. I do not detect the NT-505 introducing any sound profile into the music. That is done by your other components if at all.

I am using a Backert Rhumba 1.3 Extreme with the TEAC NT-505. I have also used it with an Onix Melody SP3 Integrated Tube Amplifier in which I use the TEAC as the volume control point not the integrated and this sounds really wonderful also. I have never used the headphone amplifier but I understand it is very good.
@axo0oxa well mate that i some fin kit you are connecting.. i am looking to roll with the chifi tube preamp...anybody got a point?

Can It play DSD files via Ethernet connection?   Thanks 
@macaw Yes, it will play DSD files.  I tried playing my Santana Abraxas DSD files the other night and it sounded glorious.
Newbie to streaming. I have a McIntosh C2500 built in dac. I am looking at the Teac Nt 505 but don’t have Ethernet at this time. Would it make sense to either have Ethernet installed if possible, or go with Teac and Node 2i for the nodes WiFi connection and its app ease, or go with node 2i and use McIntosh dac? What would be your 1st two choices?
All you need to have a wired connection for the Teac is a $20 WiFi extender from Amazon.  They have an ethernet jack at the bottom.  Teac is several levels above the Node in sound quality and I have had both in my system at different times and still own the Teac. 
@jackd I tried going that route with my NT-505 and had nothing but problems. I stream 4K Vudu and Netflix and all kinds of other stuff with no issues over wireless but I could not get the Teac to work unless I used a wired connection.
I did it for a while with a TP Link WiFi extender and now with a cable from an Xfinity Pod.  Never had an issue with either.  
It might work. It might not. I used a TP-Link WAP. Don't know why it didn't work. Everything else did. Could have been something with my network. Who knows?
Clarify. Are you trying to upgrade to a better DAC? If you are happy with the DAC in the C2500 you don’t need the NT-505 you just need a WIFI streaming device to connect to the digital input on your C2500. Plenty of WIFI streamers to select from.
I am a fan boy of the Node 2’s. They work great with WIFI and I personally like the BlueOS app that controls all Blue Sound products. Have two "higher end" systems with a Node 2 in each connected to external DACs. Love the sound. You can buy a pre-owned Node 2 for a couple of hundred bucks. I have yet to find a good justification to upgrade from the Node 2 to the Node 2i.
I use my nt-505 with an Ethernet connection now, but in a few years when I hope to upgrade to Bartok in my main system, I’ll move the nt-505 to my secondary system and use a Netgear wifi extender there, and run an Ethernet cable from the extender to the nt-505.

Currently in secondary system have Cambridge Azur 851n streamer/dac and separately Bluesound Powernode 2 (use them separately, mostly Azur, sometimes Bluesound), both wirelessly connected to the netgear wifi extender. Get dropouts rarely (once in 10 hrs?) on that secondary system. Absolutely never get dropouts in main system with Teac connected (Supra cat 8 1m Ethernet cable) by Ethernet to Netgear cable modem.

The nt-505 destroys each of the other two streamer/dacs in performance. Not close.
Someone in this thread did mention Teac CG-10M, anyone has experience using this master clock? Need some opinion from you.

I did buy a cheap master clock ($300) hook up my Teac Nt-505, the result is not so obvious, almost undetectable if not doing A/B comparison.

I do not have personal experience with the GG-10M. I have read on another forum that if you are doing critical listening of orchestral music with evolved speakers, the GG-10M will keep the music together "better". I listen to mostly rock, some jazz and some orchestra. My clock swapping is undecipherable ... everything sounds the same on my lo-fi. I am not sure if the GG-10M is intended for actual studio use.
I can confirm that the Teac NT-505 can play files from a hard disk (not just a flash drive) through the front USB port. I have a Seagate 2tb that connects OK, although it takes a while to read the files, before it appears as a library in the Lumin or Teac HR streamer app. I only have 100 gb of files on the disk. It may well be that the Teac will fail to read the disk, above a certain limit. That happened when it was connected to the front usb port of my Tascam da-3000. Not sure of the exact limit (300 gb??), or the reason, maybe the file system, the name space, or whatever. Remains to be seen if the Teac has this size limit in my case also, as reported by 1extreme, above. Anyway, the Teac can playback from usb hard drives also, up to a point. Not just flash drives, as discussed in the manual. 
I have the Teac CG-10M. To my ears there isn't a noticeable difference with or without. Save your money. Or buy mine. 
Testing the headphone amp:I need a long extension cable to enjoy music from the NT-505 from my listening chair, or the sofa. So I bought a standard four-pole (TRRS) 5 meter extension cable to test, with Fiio EX1 earplugs and AKG 450 over-ear headphones. Price: ca 15 usd.
Result: in all cases, the extension cable reduced the sound, compared to the plugs/phones plugged direct to the player. The main effects were 1) lower volume, 2) less treble, and 3) less dimensionality in the music, a bit more of a "tunnel" presentation. However, the differences were interesting.

1 Playing from a mobile phone (Huawei p30 pro): the extension cable gave a clear degradation of the sound.
2 Playing from the Fiio X3 g2 DAP: same thing, but not so much as with the mobile.
3 Playing from the Teac NT-505 headphone out: again, I hear the detoriation, but less than in case 1 and 2.
In sum - this type of cheap extension harms the sound, but to varying degree, related to the headphone amp and output.
I have no idea why this is the case - I am no engineer - but I guess that the greater "muscle" of the output in the Teac plays a main role, as well as the better detail.
Does anyone know of a long extension cable that does NOT noticeably harm the sound? (Balanced, TRRS, four-pole).
It is a bit strange that the effect is so strong, since "balanced cable" in audio usually means that long runs are no problem.