Ok, odd problem. Don't know if anyone else has experienced this or has suggestions. The gain button on the door of the STE was working fine when I bought the car. I could actually hear a pretty significant difference when I raised and lowered the button. Well, the little amber indicator inside the button went out a couple of weeks ago. Needless to say, raising and lowering the button isn't doing anything anymore. I tried swapping the switch itself, AND the amp behind the stereo. Still nothing. What else could it be? Is it from the amp? Is it possible both the amps I have were bad?
Is the amp getting 12v power? -- there should be six wires going into the amp (gray, tan, dark green, lt green, white, and pink) and the pink one should be +12v. Also check the ground coming off the amp... Out of the 5 wires coming out of the amp (black with lt blue trace, lt green with black trace, dark green with white trace, ... well there are more but make sure the resistance between the black wire with light blue trace is low.
I'm looking at the schematic-- If you need more things let me know.