Pros: Solid State Amp, Powerful and Neutral. Good software and warranty. Cheap enough to buy on a whim.
Cons: Wont Drive Some Cans Adequately. Unshielded. PC only.
First off I consider myself a music lover, I am not a true audiophile but I do have pretty good taste in sound. I can play and tune several instruments by ear, I can play several brass instruments very well and can generally tell when things don't sound right. I don't have a lot of audio equipment but I am slowly amassing a collection. When I bought the card my only pair of quality headphones were HD 515's (not a lot of love for these, I think they sound good though a little dark)
The reason for buying the card, well it was cheap and I needed it. My new headphones were proving too much for my onboard sound card and I didn't have a lot of money to spend on a new card. Not liking my current sound card much anyways, I decided for a new one. I wanted a stand alone amp as well, but just couldn't afford it at the time. With some research I decided on a Xonar DG 5.1 version.
After a simple install I plugged in my headphones and was pleasantly surprised. I really did notice a difference in sound and it seemed to drive my headphones a little better. After tinkering in the included software I discovered the dedicated headphone amp feature. I realized (whilst listening to music mind you) that I had my card set at the 16-32ohm setting on the amp. Not thinking I immediately changed it to the 64-150 ohm setting and scared the crap out of myself by instantly tripling the volume to deafening levels.
When the ringing subsided I went back to my music and noticed that there was so much more punch in my music. The bass on the 515's went from "meh" to very mean and tight. A similar effect was had on the mids. I noticed a little more sparkle in the highs but these phones are known for being dark. Volume needless to say was pushed to levels I didn't know possible to actually hear. So much volume...
The card has been spot on reliable for over two years now. It has no hum or hiss from the other components in my computer. That being said my computer is over considerable quality with a very efficient and well built power supply. If it was in say a very cheap PC that story might be different because the board lacks shielding and the general buzz of a power supply or any noisy caps could effect sound quality.
Over all I really like the card, it EQ's well with the included software. It can be used for 5.1 if you was so inclined. The onboard amp seems neutral with all the phones and speakers I have hooked up to it. It lacks the high end features of Xonar DSX but at $120 cheaper who really cares? If you are going to run 300ohm+ can's the DG isn't for you but I can see these driving 100ohm cans with ease.
If you want one shop around, you should get it for $30 or less shipped.