I ran an airhead amp w/my Beyer DT-250s for a long time. The end result was tininitus.
Honestly, if you dont have the ability to change the way your mic behavies remotely (ala nice stereo mic w/adjustable polar patterns), you dont need cans in the field.
but for home use, yea, the airhead makes a BIG difference. In the field, it will give you the volume you need if you want to get louder than the ambient noise level. They are certainly worth the money. Just be careful w/these things!
btw, the matrixing feature is pretty cool. I believe what it does is pre-mix the stereo signal (to what degree, I don't know) so that you are not getting a striaght left/right feed that your brain has to then mix into the stereo "picture".
What this is supposed to do is create a very relaxed listening session, and I thought it worked very well. Listen to it with normal L/R stereo output, and then kick in that matrix feature and you can feel your scalp and head just sort of relax. It was cool.