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.
I do not agree with this. I owned the Lumin U2 (full version) and ended up selling it, because I preferred the sound of my purpose built PC with linear PSU, especially with the Matrix converter, but even without it. A streamer is essentially a low powered PC with a decent power supply running a single application. Other than this, there is usually not much substance to the "optimised for audio" claim. In fact, I have found that higher powered CPUs in NUCs and other PCs generally sound better than the very low powered CPUs used in most streamers and "audiophile" PCs.
I also forgot to mention the Bricasti M3 in the list of DACs that I have owned. It is a very good DAC, but in my opinion the Weiss is significantly better. I have also spent time with a Meitner MA3 on dealer loan, and again felt that the Weiss was better.
But I would not discourage the OP from listening to any of these DACs, because personal preferences vary.