Audio Systems: No high output /only lows, intelligent reply, rca jacks

Question
My brother has a pioneer DEH-P640 hooked to 2 punch amps.  He hooked his IPOD up to the rear RCA jacks and now he has no high output.  All you can hear is base now.  Well obviously the RCA jacks are output only.  What do you think is damaged in the radio?  Where can I find a wire schematic?  I already have an install manual.

Thanks

Answer
I would have to know more about the installation to give you a very intelligent reply.

However, if the speakers are coax or 2-way, the tweeters may be blown from overpower.

OR, if the system is bi-amped, check to see if one amp is down.

OR, if accidently threw the subwoofer switch on the amps whilst connecting the iPod that would make them sub amps.

Hope this helps.

Cleggsan