For those using usb out of servers direct to dac, many have found various usb filters, reclockers and better usb cables are nice upgrades. Usb ports direct off motherboards are perhaps weakest link in most music servers.
I'd go this route vs. optical network conversion in front of server. Optical conversion is most likely to work in network AFTER server. Servers are noise makers, the reason why usb filters and optical conversions after server are so effective and popular. Cleaning network prior to server only to reinstate noise produced by server is somewhat ineffective and illogical. I've even found it somewhat ineffective after treatment post server, one audiophile switch I tried resulted in diminished sound quality. On the other hand, adding quality lps to my router improved sound quality, so mixed results here.