Catscratch -- you pretty much nailed it on the head with the bass, that was the first thing I noticed.  I mostly agree with what you said about recordings, though, being a basshead, I'd go one step further -- when I want that midbass hump, I'd reach for the Mk 2's, and when I don't, I'd reach for the Mk 1's.  "Rocking out" comes to mind as to when I'd want it. 
 
Kind of makes me wonder how they'd respond to EQ...