I have just finished building my music server. Dialing in Jriver Media player now. I have decided to build the Crack and I understand that it is a high impedance Headphone amp. but I can't seem to find any glowing endorsements for anything other then the Sennheiser HD 600, HD 650 ------> HD 800. Everything else is spoken of as kind of a compromise. Is this truely a one of a kind match made in heaven? Is it that there just aren't that many High Impedance cans to choose from? or Am I missing some other options? At the end of the day, I will probably obtain a pair of 600s but I hate the idea that I chose out of ignorance and there were other options. PLEASE chime in!!!!!