The only truly feasible method for doing this in Hijack would be for Hijack to completely take over the volume controls. Completely -- not even passing the volume buttons (remote) or knob volume changes through to the player software.

It could then accurately track and maintain separate volume settings for each mixer input (AM/FM/MP3/AUX), and switch between them whenever it notices the player software selecting a different mixer input.

But where to store these?

The player software uses 7-bits each for AC/DC "master volume" memory. For Hijack to also provide AC/DC, it would need as much as four times that amount, or 56 bits in total. It can re-use the existing 7+7 bits, so we'd just need to "appropriate" an additional 42 bits (5+ bytes) of the flash savearea.

There's not much space left there to grab, and this would be a HUGE use of it, displacing other potential uses/features.

Is it worth it?