You'll probably want the HD600. I've heard both and classical, my main genre, sounds much much better on the HD600 which sound signature is neutral as opposed to HD650's laid back, dark (or slightly muddy) sig. My impression of the HD650 is similar to yours. Don't blame the source, amp, dac. The Bursons are no slouch and the MBP have a really decent DAC. I suspect you don't like the HD650's character and even if there's break in, it won't stray far from the "tree".