I suppose it is a matter of personal taste, but, I tend to find most higher powered KT88 and 6550 amps to sound brittle, with an artificial edginess (someone else might consider the "edge" (hard initial attack of the note) to be a part of "slam," and hence, desirable. One has to judge these things for one's self.
If I had speakers that demanded higher levels of power, I would actually look first at OTL amps (there may be issues with impedance and bass response, but often such concerns are more theoretical than actual), and then at solid state amps. I also find that most people overestimate how much power they really need. A lot of speakers could be driven by low powered tube or solid state amps which are reasonably priced. I've seen many demonstrations where the listener thought that a high quality/low powered tube amp sounded much louder than a higher powered alternative; I don't think the lower powered amp really did sound louder, but, it sounded more satisfying at a given volume so one was less inclined to increase volume to compensate for deficiencies.
