Monomithos,
Power requirements are so dependent on one's listening level and size of room, it is hard to say whether any SET amp will be sufficient for your needs. I would say don't overlook pushpull amps; many sound fantastic and some don't even give away any of the "magic" of SET (just ask those who listen to ruinously expensive, but incredible sounding Western Electric amps).
Personally, I don't like most higher power pushpull amps based on pentodes, like the 6550, KT-88, etc. Some pentode amps based on EL-84s actually sound good to me, though they don't have that little something extra of low-powered SET amps.
My absolute favorite is low-powered SET amps (based on 45 or 2a3). But, my speakers are reasonably efficient (99 db/w, have a high impedance, and I don't play them very loud). I do think you give up something with higher powered SETs, but some are very nice sounding. A friend had a Wyetech that used 211 tubes that sounded very good.
Now, for something completely different. While I really do like the way SETs reveal fine textures and detail in an unforced manner, there is a quite different magic that is available from OTL amps. OTLs are incredibly dynamic and lively sounding. The compatibility issue there is that they work best with higher impedance speakers. Still, I've heard them on a wide range of speakers and really liked the sound too.
