Hello TANNOY56! If you have Tannoys, you're used to high efficiency speakers. Three cheers for you! You can use those gloriously liquid low watt tube amps and annoy the neighbors. Imagine a 104 db sensivity speaker vs a 94 db spl and a 84 db spl speaker. Have you ever watched the dancing meters on some bit of audio gear? Have you noticed that a 10 db difference doesn't sound like a big deal? To play as loud as the 104 db speaker, the 94 db speaker needs 10 (ten!) times the power; the 84 db speaker (the Maggie LRS comes to mind - I love them) needs 100 (yes, one hundred!) times the power for the same loudness. If you music is cruising along at four watts, the 94 db speaker will need 40 watts, and the 84 db speaker will need 400 watts (!) for the same lloudness. Efficiency is a wonderful thing. Think aboout amplifier headroom. My maggies are driven by a 400 wpc amp. They sit atop a pair of high efficiency speakers driven by a 9 wpc 300B tube amp.
There is very little difference in the sound. Why use more electricity than necessary? Why heat up the parts in the amp and shorten their life? Get the picture? I very much admire Nelson Pass. I have two of his amps. They sound great. And they heat up my TV dinners. Ouch! Environmentally . . . ? Happy Listening!