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