Ok, thanks for the clarification on that...I see how you have it rigged now. So, I assume you are already using the optical out on the PS3 going into the AVR?? If that is the case, your pre-amp outs probably won't be the right thing as they will be outputing a processed signal that will be in Dolby Digital or DTS, and the right and left channels won't contain all the audio that you need in the sound-bar. The only other option is to try using a 'rec' rca out on the rear---not sure if they would be outputing a simple stereo signal. Also, another hope might be trying an optical out---if your AVR has that also....
Hope this offers you a few more ideas....hope you can work it out...