Hi if you look in the Zen thread you will see this well documented. In Roon only mode SPDIF is the default, and caused many of us an issue in the beta testing period
I’m on holiday so cannot send you screenshots, but go to Settings ->Audio find your Zen Stream under the Roon Ready section and click on Device Info that will pop up a web page where you can change the settings and use USB again. Easy once you know how, but very difficult to find.
No problem, that thread is 2k post’s so not easy to navigate. It is pretty much undiscoverable if you don’t already know about it, or has a friend that does