Rubbish.
Its an active head unit. The AMP controls the volume, fader, bass, treble, etc. through the TX+/- multiplex from the front controls of the HU. The HU is the audio source and controller only. Nothing to do with the L/R bass, volume, etc. at that level - the level and equalisation is constant at this point.
well this is weird
When I did my head units brain change I was drivin around without head unit for a month.
I conneced ipod directly to cars stock amp and listened it with no problems. volume was controlled from ipod and thats it. all I had to do was to connect one wire to ignition, just like remote wire to any other amplifier, so it knows when to turn on or off.
I dont know what you have there, but I am telling from my experience.
Now I dont have anything from stock audio left in my car.
Now my stock amp can be used as a normal, standalone speaker amplifier.
btw cars stock navigation worked fine without stock head unit too.
my car is year 2000, is200, 8 speaker audio and navigation