The new mapper support in the latest Cyclone version seems to work just fine. However, I don't know if this is a change in your code or the regular GPGX code, but the sound emulation seems a bit iffy. The sound effects on Niutai's games in particular sound like they're possessed by demons for whatever reason. P.S. Like the new domain.
Adding to this, I wonder if it would be possible to add the option to toggle sound hacks that more closely mimic the Firecore units? Like making PCM samples always play at a specific rate, pitching the FM down 4 semitones, pitching the PSG down 7 semitones, possibly etc?