I have a Behringer headphone amp too and I'm using AKG headphones. I find that it's difficult sometimes to make the phones loud enough. I'm seriously thinking of turfing the Behringer for something better like an OZ headphone distribution mixer or something along those lines. My guess would be that the headphones are fine, and as long as the send on the board isn't too far up, the prime suspect would be the Behringer. But then there's a reason why you (and I) only paid $100 for it!

Yeah. That's my line of thought too. Especially since I'm not actually obtaining any extra volume from having the Behringer in the signal chain at all! I could wire all the tie lines for headphones so that they sum the signal and chuck the amp out. But I still get distortion at a similar level with the desk sends hooked up directly.

Do any of you technical folk know the impedence logic behind this?

stef, I have two different models of AKG cans, K100's and K66's. The 100's are roughly 100 ohms, the 66's about 35 ohms. The 100's will distort long before the 66's. Since resistance and voltage are intrinsically linked, this makes sense. Signal is represented as voltage. I use the Furman HDR6 with the independant submixer modules, so it hasn't been a problem, as long as I'm not combining the two models on the same module. I suppose you could build a pad between your Behringer and your cans with power dissipating resistors, close the gap between output impedance on the amp and input impedance on the cans.