To answer the second half of your question - to me the Mainline has better resolution and speed, and more punchy bass. It also has a more black background. I find it sounds very natural without sounding like it's "warming up the music with that tube sound". One thing that strikes me is that recordings through HD800s and Mainline tend to sound very close to a live feed. In contrast we had AKG K1000s with 300Bs running them right next to an HD800/ Mainline rig at the last Head Fi meet. That setup was like a great Chardonnay - fat, rich, powerful. To my ear very entrancing, but not necessarily "real". It drew equal praise from listeners. I would put Crack a little more toward that direction, though not quite as much as S.E.X.
The upshot for me is I prefer the Mainline with HD800s.
