Gecko Code for Twilight Princess (Wii)

[Shonumi]

Theoretically, one could code this into Dolphin with a bit of hacking at least for Zelda ucode games (dunno about AX ucode or any others). The Parameter Blocks for the Zelda ucode have 16-bits that describe whether a sound is music or sound fx. You could arbitraily set all processed sound data associated with PBs describing music to a lower volume during mixing.