Ahaha, I was right! I disassembled the driver (SMPS 68k Type 2. Code starts at 0x26F98), and it does use FM drums! It probably uses the ADPCM chip for SFX, since the original DAC SFX code is replaced with something new. There are even two unused drums that aren't listed in the table! Edit: Here's the disasm, if you're interested.