Routing Audio Using Line In

Here's my setup:
JR Media Center using 4 Zones with sound card #1.
Sound Card #1: Motherboard (AC97)
Sound Card #2: Turtle Beach Riviera (S/PDIF)

I took the motherboard sound card(AC97 - 8 speakers) and made 4 zones out of it in JR Media Center using the side, rear, center/sub, and line out. And that works perfectly.

In HS, I choose the Turtle Beach Riviera sound card and I have a cord going from the Front out of the Riviera to the line in of the AC97 but the only sound that comes out when HS speaks is on the line out of the AC97. I would like to get it so that all zones could hear the HS sound. Any ideas, things to try, or places to look for this answer?

Thanks in advance.