I have exactly the same EZBus device, and I never had any problems with (this part of) the USB sound thing.
One thing that I did and that hasn't been discussed here is that I do:
+ "Modify Instrument and busses"
+ Select "Make instrument reflects MIDI setup document"
+ Click OK
+ Save the prefs again.
And my settings stays pretty much as they should; I must say I haven't played a lot with the audio part of MIDI recently, but as far as the settings are concerned, they stick
I don't have a special driver either; plain stock 10.2.6!