Karl,
I have the NCMS Rhythm Revelator w/.5 dB matched drivers & external XO. I absolutely love them! Could not be happier. The XO's have always been external, so I can't answer your question from an empirical comparison perspective. The primary reason for the sonic improvement, as I see it, is that the external XO doesn't get the mechanical thrashing from the drivers that the internal one does.
I have listened to prototype speakers being compared on the internal/external XO basis. The external won hands down. It was much less "congested" sounding, and dynamics and harmonic texture benefited too. I know you can turn a $1599 kit into a $2000 kit with a bunch of "options," (the external XO adds posts–mine are bi-wired from the get go–,extra cable, & enclosures for the XOs) but if I were you I wouldn't think twice about it. The advantages are very audible and real, and very worth the money.
I'd go with the Revelator before the Unlimited. I'm certain that the latter is a very, very fine speaker, but, IMHO, the Revelator sounds even better.
Last but not least, if I were to do it over again I'd just get the Signature. I really don't have a single complaint about the Revelator, but if there's an improvement to be had I'd pay a few extra bucks.
Let us know how you like those Taylor enclosures. I've got some home brews. They look pretty darn good, but not perfect. I'm always toying with the idea of buying some of Taylor's. If anyone out there wants some inexpensive (like materials cost) "starter" enclosures for the Rhythm let me know. We may very well be able to work something out.
BTW, I have a balanced DS Pro Gen Va with 24/96 upgrade & I'm getting some Pythons for comparison to the 89259/89248 combo. We may have somewhat similar sounding setups.