i have a pair of Polk db 4" in the dash, and a pair of 6x9s in the rear. I have a Sony ES 4 channel amp, and want to add a sub. can i use 2 channels to run the four full range speakers, and then just bridge the othe two channels to run a sub? if so, would I just hook one 4" and one 6x9 together to make a left side, and the same for a right? this would make a 2 ohm load, correct? the speakers are 4 ohm. thank alot.