@mos_8502 might be worth digging up Famicom and SNES schematics then, I remember they had implementations but don't recall how they differ. Too much pain to think clearly
@elfi From what I can tell, the Famicom just sends the audio to the cartridge, which either handles mixing or passes it through unchanged. The SNES uses opamps to mix three audio sources.
@mos_8502 the latter might be viable then, if you can source the parts without too much cost
@elfi That’s what I’m thinking. Opamps are cheap. There has to be one in production that can be used to mix two stereo signals.
@elfi I would like it to have. I just don’t know how to design that.