me thinks voltage is going "backwards" in your system
somehow your acc line is being populated with voltage from the pc
and somehow that is causing the remote to not work (interference is a strong second in this one)
I would suggest popping a diode in the acc line to allow current to flow one way (ie to the PC and not the other) now the trick here is to not put too big a diode in otherwise the opus will keep seeing a low voltage and begin a shutdown process.........(not sure without an OPUS in front of me if this is the case if the acc line drops low in volts or if per + is the monitored line)
try a diode and see what happens, either way it will prove / disprove mytheory and you can begin looking elsewhere..... good luck
