Canterbury GR are by far the best out-of-the-box sounding Tannoys I've every heard. No surprise to me that you've enjoyed them so long! Tannoy voiced these near perfectly. That said, my crossover experiment with Kensington GR (smaller system) has me wondering what could be done even on Canterbury. Haven't asked Mark @ mainlytannoy yet about options for other SE and GR series Prestige. His Kensington GR xover is awesome. First I bought the "standard" VSA version (Clarity ESA caps) which was excellent, and just recently got a 2nd pair with "extra-premium" all Clarity MR caps - that's even better (worth the expense ~ $1300 a pair).
I only went this way out of necessity, after acquiring a "Black Ash" edition of Kensington GR (originally sold thru Upscale) which sounded wretchedly awful stock, for some reason. Its xover was the largest part of that. If they had sounded like they should (I previously owned Kensington SE, and these GR were FAR below that level of performance), I wouldn't have gone looking. But now with the Clarity MR xovers - damn if I don't prefer some aspects of the Kensington GR's sound, past even Canterbury GR. The stock Canterbury GR are probably still better overall, but damn it's impressive what these modified Kensingtons can do.
I also have Canterbury SE (becoming a bit of a collector lol) and those seem ripe for an xover upgrade too. They're wonderful speakers, but voiced a bit on the dark / chesty side of things versus other SE's and GR series.