Have you checked out www.head-fi.org? They sponsor a set of forums dedicated to headphone users, including a forum on headphone amplifiers. With a little searching you'll probably be able to get some specific recommendations for your particular headphones. Good luck.
ASL's MG Head DT OTL, now in MK III version. (MK II and III have separate power supply.) You should be able to find a used MK III, and certainly a MK II, for under $300.
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