Best gaming sound card w/ Dolby Digital?

I have gone through a ton of sound cards and all of them seem to disappoint me. I started with the Audigy 2 (no Dolby Digital), switched to the Razer Barracuda (couldn't get it working with Windows 7 beta), and am now using the Auzentech Prelude (really lousy Windows 7 x64 support, and my sound cuts out every once in awhile).

My #1 concern is quality surround sound via Dolby Digital. Basically, I have the Astro A40 audio system (Dolby 5.1 to Dolby Headphones decoder) and need a GREAT sound card with Win7 x64 support and optical (or coaxial) digital out.

Does anyone have a suggestion? Should I even bother with using the Astro A40 decoder, or is there a sound card with better "3d sound via headphones" support? (I have tried the X-Fi 3d-headphone sound support on the Prelude, and find the external hardware decoder to sound better).

Long story short (too late): When I use the A40 headphones/decoder setup on my XBox 360, it sounds great, but the 3d sound isn't nearly as good on my PC Gaming rig.