raymond: those are on the same I/O ports, so it's the same as using 2 Music Modules.
The Panasonic FS-CA1 has I/O port auto-configuration. The BIOS each cartridge will check the available I/O ports in the C0h~C3h range and configure the cartridge accordingly. AFAIK, openMSX is already emulating that.
Behold the importance of the BIOS AKA (old) device driver.
