I have been demonstrating the difference in formats at trade shows for years. My equipment has always been resolving enough to easily hear the differences, even USB. I even hear a difference in AIFF and uncompressed FLAC compared to .wav.
If you are using UPnP, then you should try Linn Kinsky and Minimserver with BubbleUPnP as proxy server, if you are not already using these.
Also, here are some killer tweaks to make Ethernet sound stellar:
1) AQVOX switch
2) 0.5m Wireworld Platinum Etherenet cable
3) EMO EN-70e isolator
4) 1.5-2.0m Wireworld Platinum Ethernet cable
Steve N.
Empirical Audio