Planetside 2 is what I'm mainly playing at the moment. My sound card is an X-Fi ExtremeGamer. I don't believe anyone claimed in this thread that either of the Sennheisers resulted in surround sound instead of stereo, just that they were pretty high quality and were given a recommendation. But I'm still looking for surround recommendations, not stereo recommendations.
As for my claim that "directivity" is better with 5.1 headphones, here's my personal experience with it...
In the past I used to use these 5.1 headphones:
http://www.newegg.com/Product/Product.aspx?Item=N82E16826159003They cost $65 in April 2005 (using Newegg's order history feature) and they actually enabled me to identify sound directions in games with a very good amount of precision. However they had crappy sound quality and the USB power resulted in a lot of buzzing. And eventually they just broke, one of the ears just snapped off after a year or so's wear and tear.
In July of 2006 I replaced them with the Sennheiser HD 555s:
http://www.newegg.com/Product/Product.aspx?Item=N82E16826106392 . Now those sounded great, and still do sound great today. The $65 headphones cost me $4.33 per month for 15 months of use. The $126 Sennheisers (which now are hard to find and go for about $170) cost me $1.59 per month for 79 months of use (so far). They are just stereo but as my primary game of choice at the time was World of Warcraft, locating sounds didn't matter much to me. However, when I did play FPS games, mainly during lan parties, I distinctly noticed that I was being handicapped by only having stereo sound.
It is most definitely real, and not a gimmick. The surround headphones actually work, actually enabled me to locate sound sources in games far better than stereo headphones, particularly first person shooters.
Now that I'm playing Planetside 2 primarily, I'm back to wanting to locate sounds well again, as its a FPS (mostly). And as I've been burned buying low quality gear in the past, I don't mind buying something decent that will last for a while, as long as it meets my requirements.
I'll look into the Medusa 5.1 and the A40, thanks!