Looking at your soundcard, and mind you, I'm not familiar with it, my guess is that it's not going to even come close to powering any of these headphones. Your 555s would probably sound better without a proper amp.
Also, what are you using for music files? CDs from your computer are are you ripping from cds? Unless you're going to use high bit rate rips, it's not going to sound good.
As to the fatigue issue you talked about, none of these headphones are fatiguing at all. You'll be able to wear any of them as long as you want with no problem.
You mentioned possibly getting the 800s. If you have that kind of cash, I suggest getting a better source and amp.










