So you're saying that you don't need an amp with an X-Fi card? Because that's mainly the reason I bought the amp forI have the HD-580's, and in my opinion you don't need more amplification on the sound card. At least in my experience, my Audigy 2 ZS drives them just fine. I would guess the X-Fi output circuitry would be very similar.
As for what you can expect, expect MUCH better sound quality. But also expect dealing with a very long and uncontained headphone cord. It's easy to roll over it with your chair or step on it to send your headphones flying to the floor. My cord recently failed after about four years of use (and abuse) and I'm still looking for a shorter replacement. Also expect the 580's to leak a lot of sound, due to their open-air design.
The main thing is, be careful with the cord.
I have a question about the grills. Do they change anything when you're listening or are they just for aesthetics. These headphones will be hooked up to my amp which will be hooked up to my pc (throught the X-fi front bay -> sound card) 99% of the time for movies, games, music, etc (don't think there is much else ). My question is did I waste the money on the amp? And my next question is will the amp do anything to my soundcard or bay. I'm thinking that the boost it will give to the HD580 would have some kind of effect and could have a possibility of frying my sound card. That is purely my thought as I am a novice in audio compared to the majority of people who work with audio components everyday. I really want to thank you guys for taking your time and letting me know what you thinkthe HD580's are much, much better... and they really, really need to be amped to reach their full potential.
I was just listening to mine through this setup:
Zhaolu 1.3 (upgraded clock, psu, op-amps)
SolozAudio Silver 16 IC
Little Dot II+
HD580 w/ my own version of a Cardas cable & HD600 grills.