I don't have any info about the matching of the Diluceo w/ the Newforms, but I do own Newform 645's and also the 630.
IMO, I'd never go back to having a center chan.
Also I recently built the GR Alphas and they've replaced my 645's as my main speakers. I did a review of them if you search the Critic's Forum if you're interested.
They're better in pretty much every way. A smallish but clear margin on the 5' Alphas Neo 8 planar section vs. the 4' Newform quasi ribbon.
The woofer section and the blending of the two halves was a FAR bigger diff. w/ the Alphas nine 6" Scan-Speak-ish woofers vs. Newforms dual 7" Scan-Speak 8545's.
Since you built your own Newform cabinets, I just highly rec. you consider selling them and building the Alphas instead.
I really liked the 645's (still do) but I got sick of having to sit at the exact right height to line up w/ the middle of the bottom ribbon section, and no placement stopped the lower notes from pulling downward, and 8' tall bass traps didn't totally fix room modes.
The Alphas eliminate all those quirks/probs and are far more eff. and can handle far more power. And the sound quality shows it.
Tonally they've pretty close.
If I considered a center speaker I'd probably get the Diluceo or VMPS's LRC, or possibly make my own out of a couple Alpha woofers and Neo 8's
w/ a digital x/over.
You know Newfrom has a little 8" ribbon again. It's REALLY expensive though IMO. Usher makes a cheaper Scan-Speak 8545 knock off that's supose to be identical to the actual 8545. Maybe a pair of those and the NR 8" in a custom cabinet w/ the digital x-over John Mayer sells?
I still say you shouldn't get a center at all though. hehe