This firmware update fixes two things:

• The PSG frequency register now updates when only the low-byte is written to. This is uncommon on VGM files for "real" genesis games, but occasionally occurs on some homebrew tracks, causing the PSG to sound out-of-tune or flat out incorrect. Thank you to @natarii for solving that issue and graciously sharing your solution.
• FM channel muting has been fixed. Previous versions were targeting incorrect key-on registers.