I'm using a Recon3D PCIe, and before that an X-Fi PCI (which I did not like much at all, especially once Windows 7 came about). The onboard audio on my motherboard (Intel DX48BT2) had unstable drivers in XP, and has been disabled in the BIOS for years as a result. I have no idea if the drivers would or wouldn't be an improvement in 7, but they caused a number of games to crash when the board was new, so that was a no-go. Sound quality and feature-wise it was absolutely fine, and I would have no problems using it if it weren't crashtastic. That isn't to say Recon3D is bad - honestly I like the little thing, it's easy to live with, and has been stable for howeverlong I've had it - very much a "set and forget" kind of device). My "next up" machine inherited the X-Fi because I could never find drivers for its integrated sound in XP, and while it's got them for Win7, I just didn't want to hassle with removing the card. 😊
RogueTrip2012: The new Sound Blaster cards have the same TI chipamp that the Recon3D, Asus, and a number of stand-alone headphone amplifiers use - it's *very* robust (on 14-15V supply it will do upwards of 1W/ch out into ~30R, and in one stand-alone incarnation (that has a ~2A PSU) the manufacturer stands behind its ability to drive a pair of 8R Tannoy bookshelves to "loud" levels; when installed in a PC (Creative, Asus, Auzen, etc) it usually runs on 9-12V though, so the output is more like 600-800mW, which is still enough to utterly shatter your ears in a matter of seconds)) and with something as easily driven as modern ATs you will have no problems aside from ergonomics (you have to plug in at the back of the case and it requires an adapter for 6.3mm). I had no complaints with it as a stand-alone in a few amplifiers/devices, or as implemented on the Recon3D, with a wide variety of headphones, including a few ATs. One advantage it has over many stand-alone amplifiers (especially under $500) is digital volume control = correct channel tracking. Most cheap headphone amps have pretty atrocious volume controls.