Most Beyerdynamics are terribly shrill and bright in the 5-15kHz range where most people experience tinnitus, I'd avoid those. As a general rule, spend more on the headphone than the amp for the best sound quality. HD600 have a wonderful, gentle non-fatiguing sound that is unmatched by any other headphone under $500 imo. A simple, neutral solid state amp will do nicely (e.g. O2), avoid a tube amp, it will make their sound too soft & syrupy.
Guess I will try and find a good Senn retailer in my area and give them a listen and feel.