4 INPUTS or 4 OUTPUTS? the sound should all come from the same place. if your guy is installing swtiches that you have no flip, you're doing something seriously wrong. all you should have to do is run one RCA out from the deck, into the amp, than the amp powers all 4 speakers, and the stereo should function as normally. i don't know what all this other garbage that this dude set up is. i would advise you to take this to a real car audio shop and have them sort this all out. you may want to go to circuit city or best buy, just because they are a big chain and can be held accountable for making this work.

this is how it's supposed to be