Home Audio Dilemma

Hello, maybe it's not a dilemma, but I have a cheaper home theater system and another set of analog speakers. What I would like to do is to use the subwoofer from the analog speaker set WHILE using the home theater system. The Home theater system is using optical straight from my mobo, and the analog sub would be using my sound card (HT Omega Striker 7.1) Is there any way I can use both sound card and mainboard audio simultaneously?

Seeing as they are separate sound cards, they can only recieve different audio streams. So what you hear outta one can never be what you hear out of the other. Optical connection is neat using only 1 cable, but remember Dolby Digital & thus Dolby digital Live are compressed formats, around 384 - 640 Kb/sec for 5.1 channels. Very lossy by today's standards.
Does your home theatre system have discrete anolog inputs? Your audio card probably has great anolog outputs, so you could use the subwoofer with the home theatre system if they all have analog inputs. Only cavet is that the center channel and subwoofer share the same jack for analog out. You'd have to split the stereo output so that left goes to HT center and right goes to you subwoofer.