Is powerfull Amps only for low sensitivity speakes?

@sfroth  good point about inefficient speakers hiding noise. Another thing they hide along with that low noise is micro detail. 

Not a good impedance curve for tubes, this speakers needs current. but because it’s a very nice 90db efficient an amp around 150w or more will do, but as I say one that can deliver current!

In practice this comment does not bear out. John Giolas of Wilson Audio had our MA-1 amplifiers driving MAXXs and his system got some very nice comments from Soundstage!; so despite the apparent numbers, Wilsons have been traditionally fairly easy for tubes.

Thanks for adding that. Some of the best recollections I have ever heard Wilson speakers has been with tubes. Brooks Berdan was a friend of mine and had me listen to the big X2 Wilsons on VTL monoblocks. The other system is OBGYN's system using all Lamm gear. To be honest I was close to buying your amps when I was running Martin Logan Odyssey electrostatic speakers. I was going to sell them and buy Soundlabs using your amps! I blame Brooks totally! ;)

My home studio speakers are 15" Tannoys with 97db efficiency.  Out of the 4 good amps I own, the best match is my 300w/ch Bryston 4B-SST2.  That's way overkill on power, but the noise floor is inaudible when using the balanced inputs, and tonally it is just the right match for the Tannoys.  

All I can add is personal recent experience with a 500 watt Magtech amp compared to a my 70 watt cj tube amp. I was worried the 500 watts would be too much for my 90dB efficient Spendor SP100 speakers, maybe even blow them out. What I should have worried about was having to return the Magtech!  By comparison, The cj sounded so muddy and hazy, especially in the lows. For many years, I thought the Spendor’s were slow and had difficulty with a lot of more upbeat music. Now I know it was my under powered tube amp. The extra watts gave a much more overall relaxed, detailed, rhythmically assured presentation. I guess there is some midrange glow that the cj adds, but now it is very clear that this  effect is distortion.