After a couple of evenings of doing the Default/Alternate dance I've come to the conclusion that they are different but both good. Since the toggle doesn't require any restarting or reboot, just a simple stop the playing track and then start playing again after the switch, I see this as something I might use on a track by track basis.
It is interesting that my impressions of each are opposite many of the descriptions here -- I hear Default as more energetic, more forward, very strong bass, can be a bit edgy at times with less favored digital tracks.
Alternate in contrast sounds smoother and more liquid on top with fewer hard edges, somewhat less forward, and while none of the deep bass content is missing, bass doesn't jump out at me like Default does. Overall, Alternate seems more forgiving of any high frequency harshness that may have crept into the recording at hand.
Tonight I've promised myself an evening of just listening to music before I take up the X0, 1, 2 and 3 ASIO adaptive profiles. I did take a quick aural peek at X1 and can say I like it more than X0 but at this time I haven't tried to characterize what I'm hearing, other than to say I want to listen to the end of a track when X1 is selected, not so much when X0 is selected.
Steve Z