Single driver loudspeakers

I have had some very expensive multi-way speakers and when starting to design my own I saw some single driver speakers, so I bought a pair of 8 inch alnico Audio Nirvana drivers and had a cabinet builder make cabinets using the design shown on the Commonsense Audio website.  The alnico magnet drivers had a much smoother frequency response that that of ferrite and neodynium magnets.  I was completely taken aback with these, especially when mated with my JL Audio subwoofer, which completes what I consider the only real achilles heel of single driver speakers:  bass dynamics.  They can certainly plumb the depths but cannot move air like real woofers and subwoofers. So I then sold these and bought the AN 12 inch drivers and a larger (5.6 liter versus 2.8) cabinets, and they are a significant step up in most parameters.  As far as treble, after hearing these I wonder why anyone makes tweeters, even approaching the sound of the ion tweeters in a pair of Acapellas I once had.  And the midrange is simply unreal, as well as soundstaging and immediacy.  

I unfortunately cannot answer your question about the low-powered tube amps you mentioned as I use as powerful solid-state amp and a tubed preamp and phono stage.  I would think the tube amps to be a good match with the high sensitivity and easy load of the speakers.  Remember, your amp is driving the speaker voice coil directly, and IMO, I can hear what multi-way speakers with crossovers do wrong.

Make sure , on size I had cabinets custom made with 3/4 inch 
Russian birch ply  and AudioNirvanas best 15 inch Alnico driver in 
a 5.6 CF cabinet 44Tall X 18-3/4W X15  D my wife seen that I had to rearrange our little room now I have to sell them to stop the in fighting.  I am in New England .great deal if so one has a SUV .
too bad though ,stay single,

For what it's worth, here's a relevant thread that I started a couple of years ago. You might find some useful info there, too:

https://forum.audiogon.com/discussions/single-driver-speakers-without-the-pitfalls

Rlawry,
I find it interesting that you achieved satisfying treble performance with the 12 inch single driver. Thus my question to johnk regarding the PHY-HP 12 inch. It’s possible he may not be familiar with them.
Charles,

I am using single-driver active speakers on my desktop (Sony SRS ZX-1) that sound good driven by my OTL headphone amp (Audiotailor Jade). No crossover, no output transformer = sonic benefit. I've used this (and other s-driver setups before) also to explore alternatives in my living room system. It helped me to decide to switch from solid state to OTL amplification. But I found that a single-driver approach in my quite big room (50m2) was unrealistic, and ended up with Audiokinesis front and effect speakers. Not exactly small and neat, but paired with OTL the sound is marvellous.