SET friendly speakers w/ slam?

Horns, my friend.

Good call on the Classic Audio Reproductions speakers, Tvad. Not cheap, but Oooo baby they got slam.

Atma-Sphere showed in two rooms at RMAF '07; they shared one of the big ground-floor ballrooms with Classic Audio Reproductions, and a regular-sized room in the tower with yours truly.

Duke

Look at www.decware .com You will need speakers that can do around 101db minimun with the watts you have available. for instance a speaker rarted at 95db@1watt@1meter will need 4 watts to produce 101db at 1meter, while a speaker rated at 92db@1watt@1meter will require 8watts to do the 101db.
Of course room size comes in to play as does the crossover in the speakers(the more complex the Xover the more watts are used up getting through it) Matching up speakers to SET's takes a little research but is worth it!

Does'nt the question depend on output too? In simple terms, a 20+watt SET will give you more slam than an 8watt one. Tube choice is a factor too. Having had both, it is my impression that 845's are more even across the spectrum than 300B's say.
My Viva Solista, 22 watt 845 SET, really drives the 89db Acoustic Zen Adagios I use in a 20 by 20ft room. There is real, deep, tight base there. In fact, it sounds louder, with better grip, than a 180 watt SS amp I also use

Consider a custom loudspeaker you can have one designed for your budget room system and music tastes. So many new hi-eff transducers availible one can build hi-eff loudspeakers in so many ways. You could even DIY your own.