This chain has been really helpful, so I wanted to follow-up with more detail and findings.
Let me be clear, the SACD 30n is an excellent sounding piece of equipment, but I ended up returning it. I eventually determined that it probably doesn't work with USB 3.0 (I think that was the problem - I didn't have enough time to run a lot of tests). Let me be clear, the SACD 30n is an excellent sounding piece of equipment. My computer is a 2019 Mac Pro (desktop) with 96 GB Ram and a 3.2 GHz 16-Core Intel Xeon W. I have 4TB PCIE SSD storage and 16TB HD storage; and I use Audirvana so I have this part covered:
Second, music servers often have more powerful processors and more RAM than a standard computer, which helps to ensure smooth, uninterrupted playback. Third, music servers usually have multiple storage options, which allows for a larger music collection. Finally, music servers often come with specialized software that makes it easy to manage and organize a music library.
I've heard that a more powerful computer is worse for sound quality, so maybe my desktop Mac Pro puts me at a huge disadvantage. I don't really care about streaming and I'm not convinced a wireless signal would be more accurate. I'm using the internal DAC from the Mark Levinson 585, so I hope the DAC is up to standard. I've also used a Chord Mojo into the 585. They both sound good. When I put my ear against the speaker (Dynaudio Contour 20i) I don't hear any noise until I turn it up all the way. I couldn't listen at that volume even if I wanted to. When I tried bypassing the computer and using music stored on a hard drive or USB stick via the SACD 30n, I could not hear a significant improvement. I did hear a noticeable improvement when playing SACDs.
I assumed that if a computer could create issues, bypassing a computer altogether (from what I can tell, even a music server is simply an underpowered computer) would provide the best sound quality. Again, I did not hear a significant difference.
I still don't get the music server thing, but maybe I just need to try a better one. I understand I looked at the Aurender stuff, but the least expensive model I could find was an N150 for $2,500.00. The N150 does not include a DAC. A good DAC (like the Chord Qutest) is another $1,200.00 - $1,500.00. I'm ready to believe, but I'm not willing to suspend disbelief. Given my experience with the SACD 30n, I just struggle to believe an Aurender would outperform something like a dedicated current MacBook Pro (or even a MacBook Air) with a custom Linux or Hackintosh operating system stripped down to eliminate all but the necessary processes. Aurender refers to a "Audio Class 2.0 USB output", but since the actual USB chipset is not identified, I have no way to know WTH that means or whether there are any tests or measurements to support any claim of sonic superiority. I may try an Esoteric N-05 since I can find one on clearance and it seems to have superior DACs (it also has "dual mono" docs). I think that will be my last try. I can't find any credible reviews for it and the few opinions I've seen here on Audiogon don't give me confidence that it's bad or good. I may also try a PCIe USB Card like this one from Sonnet.
Insofar as USB cables are concerned, I would appreciate any and all recommendations. The Synergistic Atmosphere X Reference USB was recommended by a certain very well known online seller, but Synergistic's marketing reference to "quantum tunneling" is a complete turn-off. I'm not a physicist, but as I understand it, dealing with anything at the quantum level requires equipment that would not economically feasible for any but the largest corporations. Again, I'm willing to believe if any one has any experience with them.