Cary sli-80 owners...

nearing the end of a weekend audition with this sweet amp. fed by my metronome cd1 and driving my tyler acoustic linbrook monitors, the cary has been smooth and quiet with a decent punch.
wondering if i can expect a significant improvement in performance by upgrading the electro harmonix 6sn7s. where will this take the amp? also, has anyone found significant improvement replacing the 6922's?
also, the output tubes are 6550s and they have been every bit as different from the kt88s running in my rogue 88. not bad, just different, overall loss of slam and bass weight, but they have rendered vocals and strings with a bit more brilliance and smoothness. again not necessarilly better, but different and quite pleasing.
can the sli-80 be fitted with kt88s in place of the 6550s?
if so, has this been a pleasant change?

i'm finding it very difficult not to like this amp alot.
let me hear your experiences.

thanks in advance
I am currently using Electro Harmonix KT88s, Chinese military 6SN7s ($16 each from DIYhifi supply), and EI Elite 6DJ8s. The only traditional NOS tubes are the RCA 5U4Gs.
I have tried a fair share of other NOS tubes, and for the money, this combination is tough to beat.
currently using sylvania vt-231s, amperex 6dj8s, sylvania 5931s and valve art el34s. this too, is a very nice combo. i recommend rolling the input tubes first, then moving down the line. kt88s can be used, but i have been told (and not cofirmed it with cary) that the transformers were initially designed to be optimized with el34s (original sli-50), but they responded to the market demand for more power. haven't had the time to investigate, but do very much like the sound with el34s.
I have the SLI-80 new , just bought it in July 2002. I change the 6550 tubes to KT 88, some improvement in the bottom end occured. The amp is under one hundred hours of burn in time. I could never achieved the botton end slam on my logans-monolith II, and so I retired the amp and put it up for sale. In fact I changed all the tubes, and could not achieve the bass I wanted.