High power amplifier and small speakers??

Quality, not quantity is what counts.
Some 150 watt amps will sound like junk on any speaker while others will bring out the best in them. What do you have?

The size of the speaker does not matter. High sensitivity speakers can work with small or big amps. Detail will not be lost at lower volumes with a big amp. The quality of the sound will depend on how good the amp is, not the amount of power. In your case you will only be using the first few watts.

It's not the size of the dog in the fight, it's the size of the fight in the dog!

Thanks for your responses. What if you have two amplifiers of the same quality but different power ratings (high versus low)?

For example, Totem Mani-2s are relatively small stand mounts and you better have some real big horsees driving these or they will sound like cow patties, though I have to admit that cow patties do provide difficult impedance and phase angle curves to a partnering amplifier.

I have quite high-powered amps (McCormack DNA 0.5 monos, modded by SMC Audio, which put out several hundred watts each) driving relatively small speakers (B&W 805 Signatures) and I'm really quite happy with the setup. It took me some time to get things sounding right in this room, where I've been for about a year, but I'm enjoying listening to music these days, more than in recent times. I don't think that having lots and lots of power to spare is a problem. And once in a rare while, on a Saturday afternoon when I'm pretty sure that most of my neighbors are not in, I use a little of that power, letting the White Stripes or Neil Young or even J.S. Bach fill the room. And then, the mondo power is, um, powerful.

A low-powered amp is more likely to damage the tweeters than a high powered one. The reason is Clipping distortion, caused by reaching the maximum positive/negative voltage of the power supply on high volume settings. This causes a waveform high in harmonics, which are then routed to the tweeter, possibly burning it out.

A high power amp can also burn out tweeters, but at that point it would be so loud that you, well, wouldn't listen to it that loud.

What are the speakers and the amps. Knowing this would help us produce better answers. Regards

There is one consideration not mentioned so far. If you have a high gain amp (not necessarily high power) and a high gain pre-amp, coupled to high sensitivity speakers, you may have to operate the pre-amp at the very low end of its volume control, where there are more likely to be anomalies in channel balance, etc. Also if its a stepped volume control, the steps are typically larger at the low end and it may be difficult to get the "right" volume. Other than that, there is no problem with using high power amp with high sensitivity speakers.

Volvo: For about a year, I had the Parasound A-21 driving
the NHT Threes. They sounded fantastic together. The only reason why I got rid of the amp was because I upgraded
to huge monster Genesis speaks that were way too efficient......not a good match for the A-21, but beautiful with the NHTs.
Hope this helps.

As a general rule could one say that sound quality is diminished by using a powerful amplifier (150 w/ch into 8ohms) with small speakers (high sensitivity)?

No you can't generalize - this NOT a general rule. A powerful amp can be good. A low power amp can be terrible and vice versa.

You could say that a pure Class A amp is likely to sound better at very low ouput. In practice a good Class AB amp should work at low levels too. A Class B amp is likely to have higher odd harmonic distortion. So if you focus on topology then you can make some "generalizations".

In general you can say that small speakers don't play loud and don't have as good bass response as much larger speakers (this is box speaker physics). Small speakers generally image better (baffle physics) and are more appropriate for low level near field listening.