MTX Thunder 8302 Car Audio Amplifier "setting equaliser" Questions

...until i turn down the gain or mess with the eq or freq. there is no bass or treble settings on this amp. these are the specs for the amp: RMS Power at 12.5V: 1 x 500W @ 4 ohms (<0.5% ...

I've been given one of these amps by a friend. There's a slight problem with it though, the front rht input is far more sensitive than any of the others. It's as if the gain is turned to the max on ...