I have both of Senn HD-6XX and the Fostex TR-X00 Mahogany's (and a handful of other mid-fi priced sets: Sennheiser HD1 on-ears, HiFiMan HE-4XX, B&W P3 Series II, HiFiMan Edition S, Audeze LCD-2c, etc). Of the sets I own, the two in question are two of my three favorites. I like both a lot, and use both a lot. But they're very different sets for very different use-cases.
When I'm at home, in my sunroom, tethered to my best amp, with a...