Well I went to Microcenter and out of pure curiosity wound up with both the Asus Xonar U3 and the Creative X-FI HD USB. I brought my laptop and RX900's with me so I could test them out before I left the parking lot. I plugged in the Xonar U3 first and....no difference. Sounded just about identical to my onboard IDT w/ SRS streaming music from Google Music (what I mostly listen to). I went to plug in to the X-Fi HD and then...crap I forgot my 1/4" adapter for my headphones. Went ahead and drove home with both.
After getting home, I first tried plug-n-play with my Mac OS X install first. Crappy with the onboard, crappy with both DACs. I figured as much, as I haven't had good luck with audio quality on this hackintosh. I booted up Windows 8 and downloaded the latest drivers for both the Asus (easy to find) and the Creative (almost freakin' impossible!) along with the firmware updater for the Creative. I then installed the drivers for the Asus Xonar U3 and took a listen. Again, sounded the same. Installed the drivers for the X-Fi HD, updated the firmware, rebooted and had another listen. Once again not much different. I figured I needed a better source.
I fired up Fubar2000 and listened to some flac files via WASAPI on the X-Fi and ASIO on the onboard IDT and Xonar U3 (couldn't get ASIO to work with the X-Fi HD). I listened to the same files, back to back, switching between all 3 DACs. A couple songs I could tell just a SLIGHT difference in some of the background instruments, but that's about it. And I REALLY had to listen for it. Most songs sounded exactly the same. Certainly not worth the expense.
I then listened to Google Music again, and the quality was noticeably worse than flac as expected, but again no difference between the DACs. I played around with the equalizer and music features on all 3 DACs, switched between 2.0/2.1 speakers and headphone mode (made sure to select the 32~64 ohm option for the Xonar U3), and all 3 sounded the same.
I then decided to watch some streamed video from a few sources such as Free Online TV (or whatever it's called), and again listened flat with no equalization or filters and also played around with the filters/features on each DAC. None of them were worth a damn in my opinion and just made everything sound "fake" and not realistic at all. Standard stereo with my personal touch in equalization sounded the best no matter which DAC I listened to.
I then fired up a DVD of Transformers for a better quality video/movie file, and again I noticed just some subtle differences in background sounds on the U3 and X-Fi, but nothing to write home about and I had to REALLY listen for it.
I wanted to make sure I wasn't crazy, so I ran a couple of the DVD and FLAC tests blind with a friend of mine, and he could barely tell a subtle difference as well.
One thing I did notice was how much louder the X-Fi HD and Xonar U3 got over the onboard IDT, which was to be expected. But honestly volume was never an issue with the onboard, I would never turn either DAC up that high.
All in all, I tried music lossless and lossy with and without ASIO/WASAPI, and I tried lower quality streamed video along with a very sound intensive DVD, and no matter the settings, everything sounded the same to me (and I've been playing with them for about 6 hours now). At that point, I didn't even bother with games, because I game on my computer only a small fraction of the time (which wouldn't be worth the extra cost even if it did make a difference, in my situation). Really I barely listen to FLAC or watch DVD's. Most everything is via internet for me when it comes to the laptop. Anything "high quality" I usually run through my home theater setup anyway.
Now I'm not saying that there would be no difference for others. Obviously with different headphones or switching from lower quality onboard audio might make a much larger difference, but in the case of the Probook 4530s using easy-to-drive JVC HA-RX900 headphones, you might as well save your money. I will be taking both the Xonar U3 and X-Fi HD USB back to Microcenter tomorrow, and just stick with the onboard IDT w/ SRS (which is why I like to buy locally from retail stores, along with instant gratification lol).
Edited by c00lkatz - 11/11/12 at 12:02am