I use the my Sennheiser 600s with Musical Fidelity xCansV2 (about $280 for the amp from audioadvisor.com). I also switched the 2 6922 Sovtek tubes in the amp for upgraded Valvos, with a bit of an improvement. If your budget is that big for the headphone amp, you may get better results upgrading to Sennheiser 600 - just a thought. Good luck.
John.
John.