Auxinput one of the few who get it that usb or optical directly off motherboards not optimal. If there is one thing I'd like to get across to people it would be this. I find it inexcusable so many servers don't have optimized usb built in. Benjamin at Mojo Audio was one the few who understood this with his Deja Vu server, too bad not available any more.
Optical in same boat, only the Small Green Computer Sonicorbiter I9 addresses this.
Expect to spend more money and have more complex setup with most servers since they don't address above issue. One should ask themselves why all these usb renderers, decrapifiers, streamers exist? Because they're doing the job server should be doing.
I'm also curious about these rare dacs with optical input, interesting you prefer usb, at least so far. Is this due to your entire chain or quality of usb vs optical input on dac? I'd bet on usb input being superior as technology has been around much longer and reclockiing etc. SOP these days.