Did some experimenting with surround (S9A) but never tested it with a dolby receiver so have no idea how it sounds from that perspective
I guess most people (including me) just use that effect for extra stereo space on mono samples anyway. With a Pro-Logic Surround decoder (or by selectin "Quad" in the OpenMPT soundcard settings), these channels would simply be played on the rear channels of a 4-speaker setup.
Quad unsurprisingly works but the main issue I end up with is that the stereo surround is in such that the audio appears propagate deeper into the sound space, that is it's been pushed forward instead. It does appear to skip the LFE as well often result in weaker volumes, I'll have to maybe more thoroughly test it with a DPLII receiver. Being a SNES song Dolby Surround is it's only means of surround audio, inverse echo volumes increase the sound stage but that's not MPT related xD
thanks for feedback, this song probably isn't as complete as some of my others ("dev hell") but needs a good rest.