Here's a little demo I made, with source, of using two sound channels to output up-to 10-bit sound(just 8-bit in the example).
The technique probably isn't terribly useful on the PC Engine outside of demos, but maybe it would be usable on the PC-FX...
It should be run on a real system for best results! Mednafen has a bug in it(which will be fixed in the next release, whenever that is) that causes it to be much more staticy than it should be. In Magic Engine...it sounds absolutely weird and wrong.
http://pcedev.fobby.net/junk/pcmplay-lunar.zip
Very interesting. Indeed it doesn't work well with ME 1.0. The sound is much cleaner in Ootake, although the female voice is still rather distorded.
Very nice, but seem to take some place (1024MB)
Seem to work fine with yame...