Not by the load testing I've seen on most Japanese designed amplifiers,
All those brands tend to make sure they are designed to be accurate so they don't have their own "sound". Logically, that would make sense to build accurate equipment to cover all the bases. Class A/B amps have been in production since 1957 so it makes sense that after over 60 years the bugs have been worked out long ago. Personally, I won't purchase any amplifier if it is not accurate--if I want to change the sound, I'd change the speakers or EQ them.
The dillusion about amps is if they have more power (be it lower impedance etc.) it will sound "better". A great idea if you are aslesmen but not if you actually just want accurate sound and enough power to prevent clipping. I don't care what amp you purchase, even the ones the size of a window AC unit--if you overdrive and clip them, they sound bad. The more power that is dreen into a speaker, the farther the diaphrams move and the more distortion the speaker creates. You might like a certain loudness level and the way our ears/brain works--it can sound "better" if it is louder but the more power you punch into a speaker the more distortion it creates. Eventually, the speaker drivers will move past their linear movement and start to really distort--the point of understanding the system is to not have speakers or amplifiers that enter that non-linear range. To know what power level that is requires actual real measurements of the speaker and you can find the distortion levels at various power levels. data-bass.com does that with subwoofer systems, you can see the charts at various power levels and notice how the distortion jumps at higher power. This has been known from the dawn of speakers and amplifiers, the idea is to have enough power that the amplifier will remain linear (not clip) hopefully it generates the SPL required before the speakers start to overloaad, suffer from power compression, create high distortion and so on.
Put it this way, if the amps have a "sound" and so on--why don't audio peopl;e purchase Powersoft K20 stadium amplifiers? They can punch up to 20,000 watts into low impedance loads and if more power "sounds better" why don't stadium amplifiers dominate the market? To "know" what power level you require takes math, accurate measurements of the speakers efficiency/sensitivity output, listening distance calculations and so on. The type of speaker and how efficient it is has a huge effect on that--a typical consumer speaker might be outputing 87 to 90dB at one watt/one meter while some large speakers for HT run at 97 to 105dB one watt/one meter. If you require 500 watts to get the output you need with 87dB towers, a 97dB speaker requires 50 watts and a 105dB speaker demands only 16 watts of power. That is an incredible variation between 16 watts and 500 watts--a simple AVR would smoke your hearing at 50 watts in your living room with a 105dB 1w/1m speaker!
This is why understanding power, efficiency and distance is very important for sound systems--those guys that build arena sound systems for world tours fully understand this. Out on tour in the Middle East is not the time to require more equipment, they know what they need before the tour starts.
Most of the dogma about amplifiers is bogus, the main thing to remember is as long as the impedance of the speaker is above the rating of the amplifier, the power you demand can be met by the amplifier without clipping--you are almost done. Don't get caught in the trap of the spec game, my numbers are larger or smaller than your numbers so I'm "better". Look at the distortion numbers on speakers at 10 to 50 watts, they are much higher than any modern amplifier that is built correctly so any real distortion the amplifier makes is when it is overlocading or clipping. If the amplifier is not clipping, you are golden as the natural distortion of the speaker swamps and masks the very low amplifier distortion. I'll take a Yamaha AVR that is not clipping over any ultra-wazoo audiophile amp that IS clipping.
For the OP, just sniff around and find measurements of the speakers you wish to purchase. Find the minimum impedance charts (KEF might have them on their site) make sure it don't dip down to ohms lower than your amp is rated. If that is fine, don't crank the volume control to 11 to prevent clipping. It soure would be easier if AVRs had power meters and clip lights, they used to but I've seen plenty of expensive amps that don't have a clip light so must be a style thing or something. The two amplifiers I have do have power output/clip lights on them so no worries for party mode on occasion. The poster on the other forum used to hang out here on AVS with that same amplifier religious dogma, he used to get shut down all the time and probably lleft to spew his teachings on other forums. Relax, amplifiers are mature technology that was perfected in the last century and as long as you are not clipping it or driving really low impedance loads, you should be fine.
Here is a good test with over 30 audiophile types in Spain, it will give you a good idea real world of what works. Keep it in mind when reading about amps, cables, power cords, interconnects and the like. There is a reason all this stuff is mesured, learn what the measurements mean and at what levels when measurements don't matter. Nothing worse than throwing money at a problem and you make it worse. Enjoy the read and have a great weekend.