There's no differentiation between front/rear on a HU. A signal for "front" pre-outs will be identical as a signal for "rear" pre-outs. There's only a differentiation between right/left (stereo).
Run the patch cable to your amp and use a "Y" to split the signal to the front/rear pre-amp inputs on your amp. You can use the gain controls to set your front/rear fade.
This should help with both sound quality and the noise in your system.
And... I'd get that amp turned upright before you fry it.
