Directing bass to subwoofer

Hello,

I am using a PC (with X-Fi soundcard), an AV receiver, two speakers and a passive subwoofer.
Is there a computer program that will direct the bass to the rear channel when decoded by Dolby Surround? [it would need to filter the bass from L+R, 'add' half the bass signal to one side, and 'subtract' it from the other side, the Dolby receiver would then interpret this so the bass would come out the rear channel, where I would plug in the subwoofer.]

Any other solutions that would achieve the same effect welcome! The amp is a SA-GX370.

*solved*