Last Sunday, I did some initial critical listening for the first time using USB out from my Gateway laptop to mhdt Constantine DAC (no asynch USB TTBOMK) in my bigger listening room with my biggest/best speakers, the OHM F5 series 3.
I can compare to what I normally hear using network connection to Squeezebox Touch to same DAC via Toslink.
I went in with low expectations, essentially how close could sound quality be with little hope for anything better.
This seemed to hold true. I was pleasantly surprised that sound quality was as good as it was, certainly sound in many ways, nothing inherently bad per-se, but nothing special to distinguish what I heard either. Source was cloud based Amazon Prime Music.
All in all, not bad. I still need to do some more apples/apples comparisons with specific tracks I know well though.
No doubt for me to-date that software and source material used is a big factor for sound quality, even with basic USB. AMazon prime music and PLEX sound pretty good. Mediamonkey has been very unimpressive so far.
It should be no surprise that sound quality of various software programs used to play music can vary greatly. That's an important thing to keep in mind when comparing two different technical approaches to digital music playback. BEyond that, different programs might be configured different ways leading to even more varied results.
Others have pointed out that one thing with computer audio is the wide range of results possible. I would agree. Highly standardized approaches that are designed specifically for music, like SPDIF and Toslink, definitely help level the playing fields.
SO far, I am optimistic that with the right software and source material, even non synchronous USB using a stock USB cable can deliver very satisfying, if not the ultimate, results. THat's definitely not the case with just any particular piece of software used.