For those speakers, I suspect you need 20watts plus. I know the impedence is equally important for tube amps and I hope your speakers are 6ohm plus with no nasty dips. That being said, I think a SET would suit you nicely. Unfortunatel they are'nt cheap either. They tend to need quality components, particularly the output transformers. I use a Viva Solista, a big brute that runs very hot, but just wonderful sound, it uses 845's so is more uniform across the frequency spectrum and with more drive than a 300B. They appear on Audiogon at times for about $4000 used.
SET Integrateds
I'm considering getting an SET integrated amp. Some of the models that are intriguing are the New Audio Frontiers 845 SE and the Mastertone 845 Ref. Although these amps are not too common in the US, owners seem to be pretty happy about them. These amps are all in the same ballpark pricewise. Has anyone had the chance to hear both of these amps and have a preference of one over the other? Another contender is the 300b based KR Audio VA340, which has received some excellent reviews. I'd be curious how the KR might compare to the 845 based amps. Unfortunately, it is not likely that I'll get a chance to hear any in person for a while so any input would be appreciated. Also other suggestions would be appreciated. I have speakers rated about 90db in a small room 12x14 right now, might be adding on a slightly bigger room in the future. I'm also open to separates, but I like the intergrated concept.