Hi Bob
I used to connect my Roland Boutiques with MIDI cables and mini-jack cable to the soundcard, and I was only using the USB as power charger (like a phone). But now the MIDI connection through cables is giving me a "dysfunctional sound" (glitchy, noisy, stop&go style...) as I explained in my first post...
However, it seems I have been able to find a solution ! I am now using the USB connection directly on my laptop for power and MIDI while still using mini-jack for getting the audio to my preamp on the soundcard. Now the MIDI channel selected is working like a charm. The only downside is I lose a USB connector to connect my 49 keys keyboard... but it's not a big deal since, at least, I have a little 25keys for my Rolands (I'll move selected notes one octave to another with the mouse when needed). Anyway, I am more a producer than a piano player ?