Oooold sound card for modern gaming

So I have an Onkyo SR800 HTIB set and I have it hooked up through Realtek HD Audio (onboard). It works great for movies, perfect actually. I pass it through coax and its great.

In games however, I only get stereo; which is expected. Switching my reciever to Pro Logic II: Gamer doesn't quite cut it for me either

What is the cheapest way to get real discrete 5.1 in games? I have a Soundblaster Audigy LS from 2002 or so and it has the separate outputs that I need. Will that work in my 775 board? (ASUS P5K-E) I have no idea if PCI-e is backwards compatable

Will I be able to get discrete 5.1 or do games only do 5.1 with cards that decode EAX?

Vista 64-bit in case you were wondering, and there actually are drivers for that card on vista. Supposedly they work...sometimes

Well the HDAudio doesn't have separate outputs for 5.1; it just has optical, coax, mic, headphone and out I'm pretty sure

Yeah the 6 multicoloed outputs to the right on your image can be configured for surround sound (or other uses). Go into the HD Audio Manager and just tell it how many speakers you have, and it will tell you what ports are for what.