Car Stereos: wire splicing, worst case scenario, best case scenario

Question
i have a 96 mustang. head unit is kenwood kdc-mp225, stock door speakers(front), stock 6x9's(rear), aftermarket 2-channel amp and 2 subs. the deal is if i have all the speakers plugged in, i cant hear the subs because the 6x9's are so loud. i have them unplugged right now so the door speakers and subs are the only ones running. can i splice the rear speaker wires into the front speaker wires at the head unit? so the door and 6x9's run off the same channel and the subs solo? safe or not? or is there another way to seperate the 6x9's volume from the subs? sorry for the ramble.... and thanks in advance!

Answer
No, that wouldn't be safe.  By running them together, you'd be running them in parallel, which would effectively half their resistance across the circuit (assuming they're the same resistance), which would probably fry your deck in a worst-case scenario, or cause it to go into 'protect mode' in a best-case scenario.

If the 6x9s are too loud, I'd look into getting a deck that can do per-channel volume control, and turn them down/adjust them.

Justin