Thanks very much to several of the insightful posts, Ron and Phil in particular. I know there is no substitute for auditioning in one's own room, but some of the details have really helped me believe that the Definitions would work great in my room and I should give them a test run.
I'm curious about the Def Pros - they have been mentioned to me, both in this thread and in a couple very helpful emails I have received on the topic, and I have read the stuff on 6moons about them. I'm left with fairly different viewpoints on their necessity vs. the standard Definition - some seem to think that, while the Definition is great in its own right, the Def Pros are inevitable, while others (including, apparently, Zu themselves) think the standard Definitions should suffice in all but the most particular situation. I appreciate the inputs I've had, and am not asking for those to be repeated, but if anybody has further experience with the two, I'd love to hear about them. The Zu website doesn't really address the Pros.