May I highly recommend the HD650? Lots of people claim they sound "dark" or "veiled," but on Bottlehead gear, I've not found this to be the case at all. They sound very balanced, in fact, and have great bass. Grados would probably be a no-no for the Crack, unless you did the Speedball boards and a 5998, in addition to bigger (300 or 400uF) coupling caps. Then, you might be good to go, but 32 ohm 'phones are not really what this amp was designed for, after all.
I know the 650's are more than $100, but I got mine used for less than $200. In new condition, in fact!