Al,
Yes, that nails it. The De Capo's will dig down to around 42 Hz according to their spec sheet. While that's not the deepest of the deep, with my old Manley's at 20 watts, it would produce a good, clean sense of the very deep bass notes in some of the CD's that have been causing me trouble.
I have now proven through experimentation that the Kit 1 can produce those frequencies cleanly as well, but ONLY if I turn the volume down to considerably lower levels than what I'd normally set to play these tunes. So yes, it's a matter of the amp running out of steam with the De Capo's. This amp really needs and deserves a much more efficient pair of speakers in order to strut its stuff.
I've tentatively decided that if I go to a new set of speakers, the first ones I'll try are something in the Tekton lineup - Eric recommended the Lore or Lore 2.0 for my amp and room size. I've been reading through the Zu Omen vs. Tekton Lore thread on Audiogon, and the happiness expressed there by Tekton owners is very impressive. And although I was concerned about whether the Tekton Lore would be revealing enough to show the strengths of the Kit 1, everyone seems to feel that the sound is very musical, transparent and refined.
A'gon member sebrof lives not too far from me and I'm going to get together with him in the next few days to hook my Kit 1 up to one of his high efficiency speakers to see how the sound comes together. I'll report back to all of you!
May I say in the meantime that I'm working on another blog post that'll hopefully be up tomorrow. I am happy to report that the amp continues to burn in and sound increasingly stunning. I was listening to a James Taylor live CD today called One Man Band and the sense of being in the hall was so real it was... well... unreal. I am not given to hyperbole but shoot, this thing is fabulous. :-) If you have any kit building ambitions at all, I highly encourage you to give this a try. As long as you take your time, you can build this thing.