Good sound card for playing .ac3 files properly

[The Maynard]

My current sound card, although it plays Dolby Digitally encoded wave files in 5.1 it does not play .ac3 files as 5.1. In fact it makes it sound like crap! So my question is has everyone else had success with merging a .ac3 file into your avi's and having it play in 5.1 Dolby Digital surround? If so, what sound cards do you all use?
What I'm using right now is the onboard 5.1 sound in my Asus P4S533-x motherboard and it just will not play the .ac3 as 5.1 no matter how much I uninstall, reinstall and update the drivers. There are no other options for me to click on to enable this. All options for enabling SPDIF have been selected and all speaker profiles have been chosen with no luck.
I really don't want to have to encode a DD encoded wave file for the movie because of its very large file size. Merging the .ac3 will be much better so I can focus on keeping the video looking as good as possible.
Any HELP will be appreciated. Thanks.

[crispy]

I have a Sound Blaster Audigy 2. (great sound) By the way what are you encoding with? Try FlaskMPEG to extract .AC3 and Virtual Dub to insert. Also as a side note. The software that comes with the Audigy 2 comes with a tool to convert AC3 to WAV. Just an idea, I have yet to try a full movie.

[The Maynard]

I have no problem extracting the ac3 file and inserting it into the video. I just have problems with playing it in true 5.1 sound. Now that I'm back online I can download one of the better filters that someone had a link to here and we'll see if that works.