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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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?