I've been considering for a while buying surround sound headphones for ED. But by chance on the main forums a poster mentioned this software.
http://www.razerzone.com/gb-en/surround
I honestly did not think it would work, but how wrong I was and it has increased immersion ten fold. I used the free version for a bit, but for the extra refinement I paid the £11 for the upgrade.
If you are thinking of buying surround sound headphones, give this software a try it might save you a bit of money in the long run.