While USB and COAX are prone to noise compared to Optical, the signal transmitted between a USB device and Mojo is still digital. A series of 1s and 0s when interpreted by the device before it is sent to Mojo must be the exact data when it is received by Mojo. Of course it's not 100% correct all the time that is why things like error correction exist. With the technology inside Hugo I doubt these errors are relevant. I believe, the problem comparing optical and USB inputs of Mojo is that the devices are different. USB devices are usually Android/IOS device which may interrupt with the music player app and manifest as a series of clicks and pops. However, difference reported in soundstage, details or bass would require IMO a shift in the interpreted analog signal which is highly unlikely because Mojo must interpret the same digital data to the exact analog signal all the time. I don't know any device/transport that has all 3 digital outputs but sources being used to compare the 3 digital inputs of Mojo are also different. It's possible the difference is due to the transport used and not the inputs in Mojo.