Thanks Doc. I tell my students that if you aren't making mistakes you aren't learning anything. That's true for me as well.
So my updated advice to Karl: Check out the SEX or Smack amps. The Smack will be optimized and dedicated to your headphones while the SEX will have the option of driving a set of high efficiency speakers. If price is the issue, consider a modified Quickie.
On the other hand, you can get the Crack and some reasonably priced high-impedance headphones for a decent overall price as well. I'm using the Beyerdynamics DT770 pros with a stock Crack right now and I can't find anything to complain about. The sound is Scary-Good and the combined cost is less than almost any single piece of good audio gear.
One thing I do know for sure: There is no such thing as "buyer's remorse" with any of the Bottlehead products. They are timeless, solid, and phenomenal sounding. So you can make your choice based on price, looks, or any other preference and you will not be disappointed.