Agree, I've been switching between DCA Aeon2 closed and HD600 this morning and when it comes to lower bass the Sennheiser (EQ:d) sure has something down there but it's more like a thump.And for me HD600 never did well defined bass when boosted to Harman Levels, I'm thinking it's down to distortion. All my other headphones can do bass better than the HD600.
BTW another competitorin in this bracket is Audeze Maxwell. Costs about the same as HD600, it's a headset, has bass, built-in EQ, wireless (BT & Dongle), compliant to Harman, excellent build quality, closed but spatial qualities still on par or better than HD600... Yeah, it's a "gaming headset", but if you just objectively look at what it brings to the table you might be hard pressed to disqualify it from options.