It seems that S900 owners have no problem upgrading to the S910...so far, most (well, actually, all) of my S910 clients have been S900 users.

Either the S900 wasn't quite enough, or the S910 is a marked upgrade in these people's eyes(and ears).

A GW-8L or Prelude would be a nice compliment to an S910 (or S900)...I may even look into getting one, once Roland adds style assembly to the operating system.