Happy with USB DAC? Some rambling included..

Here's the deal, a few months ago I was at a few local hifi shops looking for some monitor speakers and was shown some pretty slick music servers. I got the bug and started doing some research into it and got going.
First I figured I would get a 192k/USB dac to replace my old one that really was getting long in the tooth(and doesn't have more than 44.1k). Since I was just giving it a try, I went with one of the Chinese ones on ebay. I was able to pick out a Burr Brown chip set that seemed to have the most consistently good reviews, and it was shipped to my door in four days.
I pulled out my laptop to give it a try. Boy, did it sound mediocre. I gave it up to being a 150 dollar dac and a cheap laptop. Though it worked pretty seamlessly. But it sounded like a tin can compared to my transport/dac.
So, we ordered some back-up HP desk-tops at work that had some pretty good spec for about 300 each. 6 gig ram, 500gig HD, etc. When they showed up, I though something was wrong with them because I couldn't hear the fan. I tore one apart and found the most unbelievably quiet fan I have ever seen. First thing I though was this would be a good candidate for a music server, then I saw that it had a digital rca-out on the back. No I was intrigued. So, I took it home and gave it a try with the cheap dac. The usb input was still pretty weak, but windows 7 was nice to use compared to what I was used to.
Then I hooked up the digital out on the sound card of the computer and was blown away! Now, there was something worth listening to! I actually thought it was better than my cd setup that costed me much more.
So, has anyone here really been impressed with the USB route, and also compared it an actual digital out for sound quality? I listened to a Music Hall USB DAC that sounded pretty good, but A couple others I heard really sounded like crap.