Upon investigating your hardware setup, I see that your motherboard, an Asus P5Q Deluxe uses an integrated SoundMAX (2000B) series chipset. You have also noted in this post that you intend to use a dedicated sound card, an Asus Xonar D2X PCI express sound card.
Solution #1. I noticed from the Asus website they say that Windows does not automatically select your Xonar as the default audio device. The website suggests doing the following:
Please go to Control Panel ---> Hardware ---> Sound and apply the settings below:
Playback ---> Speaker: select “ASUS Xonar Audio Device”
Recording ---> Microphone: select “ASUS Xonar Audio Device”
The thing is though, your dedicated sound card uses coaxial cable for a medium, where as your integrated sound on your mobo uses the standard line-in (green) port that 99% of all motherboards now a day uses, so how can you possibly be confused between the two? The only perceivable way I could see is if you accidently plugged in the (green) line-in audio connector into the back of your computer along with the coaxial connection in the back of your sound card, and you don't realize that your not receiving sound from your Xonar but rather your integrated sound from your mobo! Highly unlikely. But check your playback devices to see what device you are receiving sound from.
The win2008workstation website has an audio stutter registry fix allows all applications running (processes) to prioritize for sound. It just fixes the issue presented when your system doesn't have enough resources available to dedicate to sound and it stutters. Your problem is that your sound is not stuttering, but rather its crackling. This is indicative of a physical hardware problem or software problem. Not a configuration issue.
Solution #2. By default in Server 2008 R2 acceleration for sound is turned off. You can turn it on by going to:
Control Panel > Hardware > Sound
Click on Playback
Right-click on your audio device and choose Properties
Click on Advanced
Uncheck "Give exclusive mode applications priority
Acceleration is now enabled.
Solution #3. The final thing I could think of is I tried doing some research regarding the chipset of your sound card and one site claimed your card uses the C-Media Oxygen HD 8788 chipset, which I found a driver for in the download link below: http://drivers.softpedia.com/get/SOUND- ... WHQL.shtml
Try this resolution last if #1 and #2 below do not work. Not sure if this is the EXACT driver for your model but worth a try.
Report back with your findings.