congrats on finding your way back to the sennheisers. although, from having personally owned several pairs of both hd600s and 650's, you really should try a newer pair of hd650s after some burn in. with a good amp, they have more potential than the hd600s do I feel like. at your point, without a great headphone amp, i fully agree with your sentiments in that the hd600 is probably a slightly better sounding headphone. however if you really like the sennheiser house sound, instead of looking to a woo, you should consider the various balanced headphone amp options out there. when balanced, the hd650s are absolutely jaw-dropping, they will take down MANY MANY nicer cans. easily comparable to my $1500 dollar edition 9s. balancing just seems to tighten them up that extra bit more, add a tiny bit more refinement, and i find it opens up the soundstage even a bit more (IF you can even imagine thats possible!
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