The only thought that comes to my mind about moving to a more upscale preamp, be it tube or SS, is this... Ive found that as one moves up the food chain PRAT and resolution increase. With a good line up, and I've heard the Mac top line pre with the 501s, and those XR series (12K) speakers, it was an enjoyable sounding event... albeit a brief one.. about 30 mins.
I'd suspect the house sound of THE Mac continues to improve in resolution and transparency as one moves up.
Personally, I'd be more concerned about going tube or SS from the CARY in terms of the systems needs, and naturally my own tastes.
By that I mean, What are you shooting for?
Another note is as tube preamps increase in price they seem to sound less 'tubey' as well... and I enjoy that smack of tubeyness though not sugary or molassess like... the influence of a tube preamp in the system just seems to introduce more naturalness to it and has some life within it. IMO
i've mnot found an SS preamp which can convey such things.... of course I ain't heard 'em all either.