Soundcard/Audio setup suggestions and help

Hey,

I'm building a new gaming/multimedia computer soon and stuck on what do for audio/soundcards.

Here's what I'm probably doing for the build:

i5 3470
Gigabyte GA-H77-DS3H
Corsair Vengeance 2x4gb
Gigabyte 7950 OC
plus, case, hdd, etc...

What I want to do with the computer is have it setup in my office connected to the pc monitor in there and plus use my ATH-A700 headphones when using it in the office for gaming. I'm also going to run a HDMI cable for video to my HDTV in another room, and a Optical S/pdif cable to an older Denon AVR-1905 receiver for audio to use with the HDTV. This other setup will be used for playing movies (dvix, h.264/mpeg-4,etc...) and some gaming as well.

I'm unsure if I should go for the Asus Xonar DGX or DSX.

I like that the Xonar DGX has a headphone amp, but I believe it can't send 5.1 compressed audio to my receiver, is this correct? Or will my receiver encode itself?

Or do I need to step up to the DSX if I want 5.1 to work properly with my receiver? For DTS connect?

Will my ATH-A700's work fine with the DSX or will the DGX headphone amp really make that big of a difference?

I know I could also get a desktop headphone amp like the Fiio e10 for when gaming in my office then for the DSX, but seems to add more parts and cost. But if it's that much better then that's fine.

I'm also open to getting a different motherboard with better onboard and Optical S/pdif out or another soundcard that would make this process easier/better. I really want to keep the sound card/motherboard options under $100 as this build has of course gotten more expensive than originally planned.

Thanks for everyone time and input.