Yes opl3 has 8. I didn't say it has 4 did I . I know you could use the opl2 to make opll sounds, but the opl2 is not available on msx as far as I know.
Hm ...
It even worked with Moonblaster 1.4 when I tried (I just did not try to load any waves as that would crash the MSX)...
(FS-A1ST guts, don't mind that please ...)
The socket on the board is for the MSX-Audio basic. I managed to get it working after I NOP'd the instruction that loops on the ADPCM flag during it's init.
What are you doing!? Making an OPL2 card??
What are you doing!? Making an OPL2 card??
More like done.... It works fine, even Moonblaster 1.4 seems to like it. As long you don't try ADPCM stuffs it works fine. With the MSXAUDIO BASIC rom installed, Compile stuff works out of the bat, too.
The beauty about the OPL family (OPLL doesn't count on this this comment, of course as it's a spinoff) is that the newer chips are back compatible. You can play with the Moonsound address decode logic and have it map the FM registers at the $C0 port and old MSX Audio stuff will be able to use the chip fully (at YM3526 specs of course). On power on, the YM3812 behaves like a YM3526. To enable the extra waveforms you have to set a bit on a register which doesn't exist on the original OPL chip (YM3526).
And well, Yamaha's internal LSI code (YMxxxx) for the MSX Audio LSI is YM3801. That might mean something, too. 
