The best headphone Amplifier for the Ultrasone HFI-580

the only bass-boosting DAC/amp I can think of at that price range is the Fiio E7. There is a few others without bass boost in that price range like the Nuforce Icon uDAC-2, or for $20 more, the audio-gd sparrow (version B) I don't know if you want the DAC/amp to be portable or not but I'm guessing that its not necessary because you will be using it with your pc

http://fiio.com.cn/product/index.aspx

http://www.nuforce.com/hp/products/iconudac2hp/

http://www.audio-gd.com/Pro/Headphoneamp/Sparrow/SparrowEN.htm

Good luck on finding the right amp 

It doesn't really need one but consider looking at the Practical Devices XM4. Absolutely riddled with features and quite powerful