(You'll want to reverse it for most Sierra games...)

Why's that?
Sierra's musicians composed to the MIDI specification, according to Mark Seibert, and since the MT-32 has a reversed panpot implementation (as compared to the spec), the left and right output cables need to be swapped for proper playback of
most of Sierra's MT-32-supporting games.
I'm not sure if it was the involvement of Chris Braymen, or what, but QFGII seems to be an exception to the reversal rule (at least as far as the introduction sound-effects are concerned).