2006 lexus gs430 mark levinson

I am having an issue with the Mark Levinson amp it keeps blowing two 30amp fuses under the hood. I decided to do and aftermarket amp and speakers but i have a few issues. I can not get any signal out of the low level speaker wires from the head unit to the amp, and if I ditch the factor radio I will lose the audio on the navigation. Not sure how to solve my problems or how to repair the amp so I can use the speaker out puts from the amp. I have the amp apart and am capable of repairing it if I knew what was wrong with it. Any ideas will help

Did you happen to jump start the car right before the amp started exhibiting the problem? If so, what are the chances that you connected the jumper cables backwards? If that is a possibility, the reverse polarity protection diode is probably shorted. The diode is across power and ground connections of the amp. It will be right where the big or only plug connects to the amp. There is no speaker level output from that deck. It is a preamp level, but it is too low to be useable by an aftermarket amplifier.