Perhaps you could sell them cheap, since you got a good deal on them? Think of it as a way to pay the benefit forward.
Looking over your list again, I would also suggest you get rid of:
DT990 -- because you find other mid-low end pairs to be equal or better
Logitech H800, UE6000, and the Turtle Beach -- get a single, wireless, gaming headset that could replace all of these. I use the Skullcandy PLYR1 on my PC and Xbox and it's great. Jude (Head-Fi founder) loves it...