Daniel Johnston
Headphoneus Supremus
I am not sure I want a box which behaves differently on USB and optical.
Or perhaps the problem is coming from the source, could be a resampling or something like this...
The box behaves the same fed the same quality input. Any preferences beyond that you likely will not hear. All DACs with different style inputs (optical, coax, USB) have the potential for subtle differences in sound. The question is if you can hear them or even care to try.
The Mojo2 sounds phenomenal for what it is. Don't let the debate on the subtleties between inputs cloud that fact. You likely will not experience any audible differences between inputs as long as you are feeding it with a good source and good cables.