After you see the system lprules1962 has you can see why I trust him as a beta problem solver...
I am using a Transparent USB Reference ($695. retail )but I got a B stock cable for $425) between Roon and Ayre DAC.
Unfortunately, due to the back order status of the Roon when my streaming system was installed, I never tried the Roon w/o the USB cable.
The difference was noticeable immediately with both the Roon Nucleus and Transparent cable connected. The next morning after an overnight burn-in (part of the suggested 80 hours) it sound even better.
As a guess I would assign 60- 70% of the difference to the cable and the balance of the server.