Moving away from inefficient/low impedance speaker in order to move to a Tube Amp

Harbeth while not efficient I believe have an easy impedance curve for tubes. I think you would be fine with 20 watts or so. 

I just picked up a Jolida 302crc with very upgraded preamp and power tubes and it sounds very powerful on my Focals. No lack of power whatsoever. I believe it's rated around 40 watts per channel. This is also my first EL34 tube amp and I was expecting weak bass. NOT the case at all. I would not call it tight exactly but big and not too flabby. On the other hand snare drums that used to be just a snare sound now have a certain tactile feel to them. It's been a while since I have had tubes and I'm diggin it. Long term tbd.   

why not try one of the better reviewed Chinese tube amps some of them are quite good and you can get 50-100wpc easily. Willsenton R8 for example is quite good for the money and very well built. made in the same factory as primaluna etc. 

another option is vintage or older tube amps as the tech has not really change much in the last few decades other than refinements. There's a ton of quality use tube amps that will give you more power to drive your speakers and give you more head room. 

some examples: current adds here. 

Line Magnetic 211IA | Tube | Detroit, Michigan 48214 | Audiogon 35wpc

Black Ice Audio F22 50wpc balanced integrated tube amp | Tube | Bluff City, Tennessee 37618 | Audiogon 60wpc

VAC Avatar Super Stereo Integrated Tube Amplifier; MM Phono; Remote (35148) | Tube | Erie, Colorado 80516 | Audiogon

VTL IT-85 | Tube | Houston, Texas 77069 | Audiogon

I have an Audio Hungary Qualiton X200 matched with QLN Prestige 5 and it is audio heaven. I have owned several Ravens and would not recommend for a speaker below 92 db. As a matter of fact the best match for the Raven Blackhawk is their CeLest speakers they are great speakers, James is a excellent speaker designer and they have a gem.

Focal speakers have above 92db models. And they are pretty decent speakers. 

Right now I drive 948s with Single Ended amplifier

Although a speaker's sensitivity should be considered when matching them to an amplifier, it is wrong to use a speaker's sensitivity rating as an indication of quality. Many speaker designers opt to trade high sensitivity for deeper bass reproduction, especially in a smaller enclosure. Remember also that a tube powered amplifier will seem more powerful and play louder than a solid state amp of the same or similar power rating.