6550 vs. KT88: What's different about the sound?


I have a Music Reference RM9...great amp. I used EL34's for several years...nice match for the slightly agressive ribbons in the Newform (best imaging I've ever heard) Now that I have the Maggie 1.6 QR, the 6550 (Svetlana) sounds better... but will the KT88 better define the high end without being aggressive and better control the bass without being anemic? KT88's are much more expensive than 6550's so before I lay out an extea 300 $, or so, I'd like to know what to expect. Any help out there?? Better to get me at gymrome@aol.com. ( use "Tube question" as the subject so I know it's not spam )
jrome
Newbee,
I used to have the Svetlana 6550c and upgraded to EH KT-88.But have 2 6sn7(sylvania)for the input in the amp..If i will match the input tubes to the output tubes (EH 6sn7 gold),which will now be the same brand.As you mentioned by matching the power tubes and the small tubes,do you think there will be an improvement ?
Pescolar, What I meant by matching had little to do with brand matching. I was referring to matching the sonic's of each type to produce an end result which you find pleasing. It may be fortune or just some of my prejudices, but I have no amps where the small tubes are the same brand as the output tubes. Finding the perfect sonic match is the 'fun' to which I was referring.