Can my MC275 power speakers with 91db sensitivity

It can but probably not optimally along the lines related by Al.

That's not to say it won't sound good or meet your needs/expectations, only that you have a good chance of doing better in terms of both volume sans clipping and balanced and clean bass response and lower distortion otherwise as well perhaps to the extent that matters if you become so inclined.

So you can look at these things from the perspective of ideal technical matches that maximize performance, ie the perspective of intelligent "audiophiles" for the most part, or from the perspective of does it sound "good" or "good enough". Improving usually comes at some cost.

So its very much the oft cited "your mileage may vary" type scenario.

If that bothers you, then probably better to seek out different speakers that are more efficient and tube amp friendly in general.

Al's speaker recommendations are good ones. I might toss in Triangle and many Focal/JM Lab speaker models as possibilities.

Even Magneplanars could work very well with a tube amp like that, especially if very high volumes are not a concern.

OHM is another line that is perhaps not as tube amp friendly as some, but offers good value and decent performance with a higher power tube amp.

Adding a powered sub or two and offloading the low bass to that opens up a lot of additional popular speakers choices. That's a popular option for many OHM owners that use tube amps in some cases (some might go sans sub)and also for most any good quality speaker, including SOnus Faber.

Also, most any good quality horn loaded high efficiency speaker (mid 90s db efficient or higher) would be very good technical matches for that amp. There are many very good makers of high efficiency horn loaded speakers out there these days. Take a look at Cathedral speakers out of Virginai for an example of good sounding horns I have heard that can be had for very modest cost.

Electrostatic speakers are another good option to consider if that kind of thing might float your boat.

So basically, there are ways to make that amp work very well indeed with most anything if done right.

Hope that helps.

Elegal, ... Al, Ralph (Atmasphere) and I have been around the block on amp/speaker compatibility issues so many times, like the proverbial tiger who chased his tail and turned into butter, I feel like I'm about to turn into a stick of butter too.

As a threshold matter, let me say that Al's advice is spot on. Let me amplify what he said with a real experience. I've use ARC tube amps to drive my Paradigm 8 V3 speakers.

Although the S8s are pretty sensitive, 92dbs, they have impedance and phase angle curves that are so rocky they would make a mountain climber dizzy. To add insult to injury, the impedance curve in the bass through midrange spectrum is 4 ohms and the phase angle dips to a negative 60 degrees at one point. In short, the S8s were designed to be driven by a high current/high power SS amp. Ooopps.

Why the long tale? For some reason, my old amp, an ARC VS--115, was able to drive the S8s. Why? Here's my guess. The VS-115's rated power output is 120 wpc. Plus, its output impedance is "low'ish" for a tube amp. So the amp performed "SS-like" as a "constant'ish" voltage source.

But here's an interesting twist. I switched out my VS-115 for an ARC Ref 150. Now my speakers really sing. Why? Here's my guesses.

First, the Ref 150 has more head room by way of rated power than the VS-115: 150 wpc versus the VS 115's 120 wpc.

Second and possibly the most important. The capacitive power supply in the Ref 150 is 3 times larger than the VS-115: 1040 joules versus 334 joules, respectively. That's a lot. What this means in plain English is that when the Ref 150 is driving my S8s in the rocky road region, it can push some serious juice with its beefed up power supply.

Your take-aways.

(1) More power will not hurt, even with so called sensitive speakers. If in doubt, and your wallet can afford it, opt for more amp power. Even if a "marginally" powered amp seems ok, an amp that can handle the peaks and valleys of power demands, either relating to dynamic swings from the input source material or rough impedance and phase angle curves, I suspect your system with sound even better with more power.

(2) As Al said, first pick your speakers and then your amp. I was lucky because I did it half-arsed backwards.

(3) Read the many threads on A'gon which speak to speaker/amp electrical compatibility. Focus on Ralph's White Paper which discusses so called Voltage Paradigm versus Power Paradigm amps. Try to get your arms around the notion of how speaker impedance (which varies as a function of frequency response) can affect the sonic presentation if the speaker is driven by a tube amp with "high'ish" output impedance.

And, as I came to better understand, not all tube amps are "pure" Power Paradigm amp. If a tube amp uses NF, which as Al said will lower output impedance, the amp will perform "SS-like." Kinda like a hybrid.

(4) The use of excessive NF in either a tube or SS amp to achieve certain operating objectives (e.g., lower distortion, extended bandwidth, higher DF) does not come without sonic costs.

That's it.

I'm on board with Al/Atmasphere/Bifwynne and others regarding how impedance and phase angle are key factors to consider when choosing an amp to get best performance out of speakers.

Also that there are many shades of grey in between the extremes in regards to amp technology and design, and that as a result, it can be very hard to predict how good or not any particular combo really sounds, but it is not as hard to predict which combos have the best chances of working out optimally together from a technical perspective.

Also I believe that is is important for things to work out well from a technical perspective, however, that alone does not ensure enjoyment. Enjoyment is what it is all about in the end. Good technical execution can usually only help, but alone does not guarantee the desired outcome, which might be had many different ways.

You have received a lot of good advice from almarg and other which I would take to heart. Another way to look at thing is what amps do the vendors use to drive their speakers at demos and shows. The Sonus Faber Olympica series were in several rooms at RMAF and were all driven by solid state amplification...

I agree with the whole discussion of the difficulty of driving the original Cremona speakers and the problems of difficult phase angles. But, before reaching a lot more conclusions, I think it is important to understand if the speakers are original Cremona or Cremona M. They are quite different speakers.