Asynchronous USB vs. SPDIF with regard to DAC upgrade

A few thoughts based on recent experience. 

I upgraded from a Weiss 205 with Fidelizer linear PSU to a Weiss DAC 501 Mk II, and it was a significant upgrade. Other DACs I have owned are the Chord DAVE/M Scaler, Nagra Tube DAC, Ayre QX5 Twenty, Mytek Manhattan II amongst others. They are all good DACs, but I rate the 501 Mk II more highly than any of these, based on my personal preferences. I do not agree with the comment above that it is too detail oriented and analytical. It is neutral and accurate without artificial warmth or bloom, but is full sounding, as well as being musical and engaging. I have not heard the Berkely so don't know how it would compare. 

I have compared USB vs SPDIF and AES/EBU with the Weiss 501 Mk II a number of times, most recently in the last few days. I use a custom made PC based on a fanless NUC with linear PSU as a music server, and use its USB output either directly to the DAC, or to a Matrix X Spdif 3 and then SPDIF or AES/EBU into the DAC. The Matrix is also powered separately by a Fidelizer PSU. 

The USB input of the Weiss 501 Mk II is very good. But it definitely sounds better through the SPDIF or AES/EBU inputs (depending on the cable) via the Matrix X Spdif 3, rather than using USB directly into the DAC. The sound is richer, fuller, slightly warmer, and slightly quieter. 

Obviously, this is based on my specific configuration, and digital audio is very system dependent. 

The ethernet input of the DAC is also excellent, but again the SPDIF and AES inputs are noticeably better in my system. 

In other words, if you get the Weiss 501 Mk II - which you should certainly try to hear, because it is one of the best DACs currently available - you will need to experiment to see what input sounds best, because it is highly system (and cable) dependent. If you are using an external streamer, it will also depend on the streamer quality, including its own clock and internal PSU.

That makes sense @rossb 

a computer used as a streamer via USB is never an optimized streaming solution. Especially one that doubles as Roon Core. What your Matrix is doing is reclocking the USB signal as part of converting it to SPDIF. That will improve jitter levels going into your DAC and the final result is better sonics. 

With a dedicated streamer such as U2 Mini you get an optimized USB output that’s prioritized for audio. It’s never the case with a computer. 

It’s easy for the OP to test this. Get a USB cable that’s comparable in quality to the SPDIF that he’s using currently and compare it within his current Lumin and Weiss 204 setup. 

The 2 contenders for a dac upgrade are the Weiss 501MKII and the Berkely Dac Alpha Series 3. The are both priced within $1000.00 of each other with the Weiss being more expensive. My thoughts are that the Weiss 501MK II has a built in headphone amplifier, a preamplifier and room correction capabilities. I have the Weiss 204 which has no bells and whistles and only gives me the sound. Yes I did a $1000.00 Modwright Linear Power Supply. To my way of thinking this makes the Berkely Alpha Series 3 Dac a better value if every thing else is equal. A portion of the asking price for the Weiss must include the extras that Weiss offers. I do not think I can audition both at the same time doing an A-B comparison. At this price range would like to get this right. I would buy the Berkely without the USB box which costs an additional $2500.00, and would use it through SPDIF or AES/EBU, balanced.  Am I thinking about this in a reasonable manner?  Thank you. 

I will second @audphile1 advice to consider a DAC that supports Ethernet and serves as an endpoint. I recently picked up a Bricasti M3 to pair with my Innuos Zenith streamer using USB. On a whim I bought an Antipodes CX server at a good price and set it up as a Roon server and ran a direct Ethernet cable to the M3. There was no going back. I did all sorts of comparisons with the Zenith and USB, even tossing in a DDC so I could compare with SPDIF via AES. 

Now my thoughts are on upgrading the Bricasti, or trying the Meitner or Tambaqui, but I don’t think I will be going back to USB or SPDIF. It looks like the Weiss 501 supports this, I would give it a try, and don’t overlook a server upgrade as well. 

There are dealers that would allow a home audition if you’re buying new. 
Berkeley’s lack of USB, no network card makes it a tough sell. Being s straight DAC only it will be much harder to resell on a used market and you will most likely take a significant hit. 
I would suggest finding a dealer that can allow you to audition and compare several DACs in your system or buy with return policy.