Okay, so, I'm currently using my onboard sound which is Realtek ALC 892.  I don't have lossless ripped music, primarily my collection is 192 kbps aac/m4a, some is higher quality mp3.  I listen primarily with a pair of Ultrasone HFI 580s.  Can anyone recommend a setup that would be beneficial to me as far as sound card or amp(that is if there would be any tangible difference)? I'd like to stay under $150(top price or performance would be ideal).  I do occasionally game, but I'm not concerned with gaming audio performance.  Also should note that my board only has PCIe slots.

Perhaps a DAC + Amp combo like a Fiio E17?
 
Hmm perhaps you could get some more insights with this poster's mini review which was very recent ^^
http://www.head-fi.org/t/618594/review-ultrasone-pro-900-kees-mod-fiio-e17-the-electronica-review

An alternative is the HRT Headstreamer.  See my blog for review.  Several headfiers have confirmed it to be a bit above the Fiio offerings.