Unamped: AKG K 701 vs Ultrasone PRO 750 vs beyer DT 880

Hi, I'm going to get a headphone for competitive PC gaming (no LAN, just my quiet room), which I will hook up to a Auzentech X-Fi Prelude. For gaming clarity, soundstage and positional sound is important I imagine. I narrowed my options down to the AKG K 701, the Ultrasone PRO 750 and the beyerdynamic DT 880 Edition 2005 (I would also add the Denon AH-D2000 thats also in this price range, but I read too little about them).

As the headphones plus the soundcard is expensive enough as it is, there's no money left for an amp, but I will probably get one down the road (could take up to a year before I get one).

I'm currently using Plantronics DSP-500 with the integrated USB soundcard, and I don't really think its bad, though positional sound could be better and the sound could be more clear. I imagine even unamped the above mentioned headphones in addition to a X-Fi Prelude will still be a major upgrade to my current Plantronics.

What headphones would you recommend to me and why?

For a real audiophile, or for anyone? Like I said, I'm coming from a Plantronics DSP-500 USB headset

So I should get the Ultrasones, or save up some money for an amp and get the K 701 or DT 880?

I also play 1on1 (Unreal Tournament 3), so a mic isn't always needed. And if I need one, I will just use a Zalman clip on mic.

The Platronics are decent, but if they were good, a lot more people would be using them

Anyway, judging from all of your replies, I think I'll save up some money for an amp, and then get the AKG K 701. (Or is the DT 880 better for gaming?)

I see in your signature that you have the K701 and the DT880, which would be more suited for gaming (soundstage, positional sound, clarity?)?

Another question, which one should I get, the DT 880 PRO or the DT 880 Edition 2005, whats the difference?