If you have never built a kit, buy Crack. It is intended for first time builders and the more simple layout makes it much easier to digest as a first build.
If you have building experience and like to upgrade stuff, buy the Crack-a-two-a. It includes upgrades that, while making the build a bit more involved, you would want to incorporate. It also offers more space to add further upgrades like insanely large capacitors.
If you want the end-all be-all go to the Mainline page.
All of these amps will work great with high impedance headphones (and Mainline will work with low impedance cans too). The more premium the amp, the more resolution and control you will get. This will be audible on any good cans like Sennheiser and Beyerdynamic.
« Last Edit: August 04, 2015, 12:22:25 PM by Doc B. »
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.