split 6 volts rca or not?

I have a deh-p740mp which has 3 pairs of outputs at 6volts ;sub, front and rear. I currently have a 4 channel amp 400watts rms for the mids and highs and another amp for the bass. the mids amp is bridged so i have 2 channels at 200 watts each and the front output from the deck goes to this amp . the left rca goes and splits to the left input of the amp and the right goes to the right. i need to use rca splitters because the amp has 4 inputs . should i currently leave it this way ? or should i utilize the rear output from the rca of the deck so there will be no splits .   "I'm So Loud It Hertz"

You are using a 4-channel amp bridged into one set of speakers?  What is the make/model of the amp?  Most amps are designed to bridge channels 1 and 2 together and channels 3 and 4 together.  NOT channels 1 and 3 (both "lefts") and channels 2 and 4 ("rights.").  Check your owner's manual for the proper setup.  That being said, you definately want to send the same signal to both channels that are bridged together (NOT the front and rear, one or the other only) and yes you should use Y-cables.

I think that i wasn't too clear .. the left front rca from my deck goes to channel 1 and 2 of my amp via a splitter and the front right goes to 3 and 4 via a splitter . i therefore have 1 and 2 outputs bridge and 3 and 4 bridge on the output of my amp. what i want to know is if i should use the rear output of the deck (rca) and the front so i will have 4 pre out from the deck to go to the amp ?i will not be able to bridge my amp then . will i gain better sound quality by using 4 rca outs and amp being bridge rather than using 2 rca and splitting and not bridging the out put of the amp? the amp is a crunch drive 4004v 100rms/channel , 4 channel."I'm So Loud It Hertz"

No, you should not use both front and rear.  Use one set only and Y-cables as you have it.