Car audio issue. (subwoofers)?

[TitoOrtiz]

I recently re-installed my subwoofers into my new car. Since I used the factory stereo (which lacks RCA outs), I had to purchase a Line Output converter. I tapped into both rear speaker leads.
Here's the issue:
I am running a Rockford-Fosgate P5002 amp rated at 1500 watts max power and 2 10 inch Rockford subwoofers. If I run one of the subs in bridged mode, it sounds great. When I try to run both subs hooked up as they normally would be I get about 1/4 of the sound, even with the gain on the amp at max.
What is causing this loss in signal and what can be done to remedy it?
When I had the amp and subs hooked up to an aftermarket stereo in my previous vehicle, they sounded great, so I'm sure that my amp is PLENTY powerful enough to run the subs.
1. Don't tell me my amp is too weak.
2. Don't tell me to install an aftermarket head unit.
3. Tell me what I can do with what I stated above.

 

[bert]

When you bridge an amp it usually doubles the power that the one sub would receive normally. Say your amp is a 200 x 2 watts, when you bridge it it becomes 400 x 1. So when you split you amp back to a two channel amp you lost half your power there. Also it not all about Max power, this is only when the bass is really hitting hard. Im guessing your RMS output of your amp is 750 Watts. Check this with your two subs. if your subs need more than 750 watts together then that could be another problem.