You did not say what you ARE using NOW to drive them, and how it sounds to you.

From what I have read, it seems that a low-power amplifier might not be able to drive them adequately
with music that has a wide dynamic range.

A lot of it depemnds on the type of music, the size of the listening room, and other factors.

You are right. 30w of Class A will behave and sound very differently than 30w of Class AB. I feel like Class A amps (and Class D if it is well made) seem to have better control over the drivers than AB unless the AB amp is very high current. That being said, I have not heard the Kef LS50s driven by a lower current Class A. I would bet that in a smallish room, 12' x 12' they would sound great.

Bialator wrote:

Actually I am using a McIntosh MA5200. It is clean and nice, maybe not super open and a tad cold/dry, but just a little...

I tried with a Hegel H160, The bass was great, but the highs and mids were too far begind, like cut.

After it I was surprised by an old Pioneer A27, not so clean as the McIntosh, but there was something in the body of the sound and the "soft vividness" of the sound that maybe think that probably I need more drive.

However in the past I tried with other speakers and not always watts = drive, sometimes class A drive is different and goes along well with some speakers, so that is why I was asking if somebody tried them with class A...

I am not big fan of class A amplifiers. They produce excessive heat and seldom have enough power to drive speakers adequately. A Class AB amplifier is CALLED AB because it operates Class A at lower power levels and then only goes into Class B when power peaks demand it.

I really really love the open musical sound of Musical Fidelity amplifiers.

I suggest that you consider getting a Musical Fidelity M5si, which Audio Advisor has for $1999. It is a wonderful integrated amp and includes a very good phono stage and DAC.

I had a pair of Kef LS-50s that I used with various amps. Among them was my Pass Aleph 30, which as it's nomenclature indicates, is a 30wpc amp, in Class-A. The Kefs sounded ok but not spectacular with it. They liked a lot more power. In fact, the reason that I got rid of them was that they only ever sounded good with higher powered amps, and my amps are mostly low/mid wattage. They were my bedroom speakers and were eventually replaced by cheaper ELAC Uni-fi UB5s that actually sounded better with the amps I wanted to use in that system.