Yeah and there's the enhanced version of Zanac EX too.
But the story is clear. Some hardware developer decided to add an extra PSG. Maybe to fix a 8250 he had, maybe he knew about a friend with such a machine. It was easy to integrate into the FPGA anyway. After that it kind of became a standard, with other hardware projects copying it on the same I/O ports. And of course people started exploiting it and dual PSG was born.
The story probably isn't 100% accurate, but I like it this way. At least it explains why dual PSG is here and for instance dual (or quadruple) SCC isn't.
Xenon enhanced with dual PSG (one PSG exclusive for music and the 2nd PSG just for SFX) if you have Y8950 Audio Cartridge then you'll be delighted with voices samples.
Some hardware developer decided to add an extra PSG. Maybe to fix a 8250 he had, maybe he knew about a friend with such a machine.
Actually, the second PSG in MegaFlashROM SCC+ was meant to get a "perfect" SCC-PSG balance. Every MSX has a different sound mixer, and that's why in some models the PSG sounds louder than in others.
Games like Goonies 'R' Good Enough used that second PSG in order to achieve the same sound experience on different machines.
Also, that extra PSG seemed a good idea for future projects (E.g.: WYZ Tracker with 6 PSG channels)
And to be honest, when I released MFR SCC+ I did knew about the problem with the 8250/55/80 sound mixer.
