This is my first post to this forum. I recently got myself a IIGS, not having owned any Apple II before. I was a C64 guy back in the days. Now, my interest spans pretty much all computers of the era. Apple II was very uncommon in my country (Sweden), although 68k Macs were not.
Now to the point. I know there is hardware such as TDX Stereo card and Sonic blaster. I don't know about the Sonic blaster but the TDX design is based on de-multiplexing the sound multiplexed by the IIGS before being output. I haven't studied the IIGS schematics in detail yet and since I'm not really that good at electronics I'm not sure I'll be able to understand them.
Here is my idea, probably stupid, but shouldn't it be possible to tap the left and right audio signals and do whatever filtering and amplifying necessary before it is multiplexed? That way there is no need to de-multiplex the signal afterwards. I mean there should be losses and added disturbance every time the analog signals are tampered with. Someone should even have done this already if it's possible.
OK, now you can shoot me.