Seeking full range single driver speaker recs

Some good suggestions might be
Cain & Cain Abby w/ Fostex drivers

If you are into DIY, you could do a similar cabinet called the Voigt Pipe with Lowther drivers.

These are called "full range" speakers, but they actually omit the lowest octave from 20Hz - 40Hz. Most users don't mind this, but some use subs in conjunction with them.

They can both be driven with a couple of tube watts, and don't present any difficult loads for tube amps.

I'm sure some other folks will have more suggestions.

TWL makes some good recommendations. I've heard the Cain and Cain Abbys (w/the Fostex 166e drivers) and they are fast, coherent, dynamic and exciting to listen to. They are also efficient and easy to drive. The REL should work very well with them. Start the cutoff at about 70Hz and work your way down. Also, as a bonus they are awesomely constructed and finished.

I've also heard the Omega speakers (also with Fostex drivers), but was not too enamored with their sound.

Lowthers are in another league, but they are probably out of your budget, unless you are into diy. (Check out the full range driver website for more information on diy.)

I'm not aware of such a beast. The only manufacturer I'm aware of to make such a claim was Yankee, at a much higher cost.