Hello Hopping pulse
I had the same issue a couple of weeks ago. And I did some extensive reading !
Here's the scenario and there's nothing much anyone can do about it.
1. Good that you are connected on HDMI, that saves you a ton of headache.
2. Games are ALWAYS decoded by your computer. You cannot have them play as Dolby Digital, Iff your sound card says it can play Dolby Digital, it can, be sure you have it setup so ( You should have a Audio Control Panel - Creative, IDT, RealTek etc ). But you can always change setup in the game to 5.1 (Even PCM ) if it supports it. If your game does not support 5.1, set your AVR to 7ch Enhancer, it will give you a more immersive sound. And trust me, PCM vs DTS/Dolby does not make a big difference when you are gaming. Today's games are intelligent enough to have positional audio built into them !
3. For your sound card to play DTS/Dolby, you will have to Bitstream it. This meaning, any video you play is mostly PCM as the players like VLC, Media Player Classic stream it that way. Exception will be a 5.1 Enabled original movie DVD.
4. However you can set up bitsreaming by following the link below: http://www.avsforum.com/t/1357375/advanced-mpc-hc-setup-guide
Do PM me if you need further clarification.