It sounds like what you already have will be more than good enough.
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Most high efficiency loudspeakers get their efficiency from tight gaps and precise construction. As a result they are highly reactive and are over-damped with anything more than a very moderate output impedance from the amp.
IOW, a tube amplifier will sound better; will play deeper bass and be smoother and more detailed overall than most transistor amplifiers. This is because a tube amp, especially one with no loop feedback, will not react poorly to the back EMF from the speaker, and will not present such a low impedance to the speaker that it is over-damped (if the speaker is over-damped you can loose as much as 8db of bass in the bottom octave).
I recommend some sort of lower-powered Push-Pull triode amplifier, maybe something with no more than 50 watts. You'll find the speakers doing things you had no idea they could!
Those 15 inch woofers can sound slow and mushy with tubes.
The size of the woofers has nothing to do with the speed of the amp; this is a common amplifier myth. It turns out that if the woofers are over-damped, that that can slow them down, IOW if you have excessive damping factor the woofers can be slowed down, and the result is decreased output as I mentioned above.
Here is a reference article about this issue:
"Critical Damping: Missing Link in Speaker Operation Parts 1 & 2
I ran Klipsch Forte II's with both SS amp and tubed amp. The SS amp was 200WPC and the Tubed amp was 90WPC. These speakers were so efficient, I think they could be driven by a 3 watt amp. Anyway, I never had any problems driving these speakers with either amp. The Forte II's are on the bright side, so I preferred the sound through the tubed amp.
I have Klipsch Forte II used for Classic Rock. I used them for some time with a Odyssey Stratos and a tube preamp.
The sound was very good. I then bought a Baldwin Tube Amp here on Audiogon from Audiospec. The sound is much better, to my ears. Yes, even the bass is stronger ! My room is 14x30 and the 28 watts is more than enough to fill the room, and then some. So I think either will work, however a nice 30 watt tube amp is a lot nicer, in my opinion.