Unless you are DIY building the speakers :Speakers are rated as systems not per driver. The three speakers in the cabinet are connected to a crossover that doles out the appropriate amount of energy to each one, and only the right frequencies that it should reproduce. the speaker system itself receives a maximum RMS rating but this is a continuous high current - to failure rating. (how much it takes to burn out the speaker) normally, this is not realistic, as the average rms (Root Mean Square) wattage delivered is controlled by where you set the volume control, and peak wattage levels due to wide dynamic swings in the music are normally very short, so do not count as continuous current events. Like with a car, you "put the accelerator down only as suits the safety of the vehicle not all the way to the floor no matter what. Like cars, you control this, no amp/speaker combination is "automatically" idiot proof. At best they are fool resistant.
Most speaker SYSTEMS reach normal room listening levels at seven watts or less. Very large, very heavy and very inefficient speaker SYSTEMS will have far more snap and clarity with a bigger amp (150 or more RMS Wattage at less than .04 percent distortion rated at 8 ohms across the audio spectrum, 20 to 20,000 Hz.) than with a smaller amp, but not because you pump the volume up, but because the amp is then able to control the instantaneous movements of the cone better , especially on dynamic events ( very impulsive music) at normal room levels. For most bookshelf sized units, a solid state amp delivering 60 watts or better will be Okay. Sub woofers for AV receivers usually have there own built in amps, and are not powered by the receiver. Unpowered Sub woofers will require purchase of an exterior amp to drive it, and most often an outboard crossover to cut away the higher tones, which it cannot reproduce well, or at all. If you are buying separate component audio, get the best that you can afford, but not just in raw wattage, but also in signal to noise ratio, slew rate, THD Distortion, and size of power supply. Match that with a very good preamp. If you are into tube amps, get VERY efficient speakers with high SPL, yet the best sound balance you can find. Always audition your choices. Never buy sight unseen. As receivers almost never host more than 130 watts RMS at 8 ohms with acceptably low distortion across the audible frequency spectrum, that wattage will likely be the upper limit for any receiver purchased. If any of this is greek to you, go to a stereo review or theater sound audio magazine or site, and read up on the basics.
If you are intending to DIY a set, Use the drivers and crossovers from a well pre-planned kit or instruction set first, that does indicate what the system specs will end up being.Madisound has very good kits and plans and does all this for you. Meanwhile, consider the hobby a learning based endeavor, and teach yourself through the basics and advanced info you need, to have fun doing the math the carpentry the electronics, and driver selections, pouring over and understanding the white sheets, nomographs, and what likely need doing to compose and tweak a good speaker system. A good book going over the Thele Small equations, would be a fair start. Madisound for example, has a large DIY area, and will point you in the right direction. and No, no one here is going to "teach you" how to do this well in any probable length of post. DIY audio is about LEARNING a lot of stuff about a lot of things..
If you are attempting to repair a KEF speaker (model unknown, you did not say) by replacing damaged drivers, most hobby sites Like Parts Express, that sell such, have help lines that will try to select replacement drivers that are a fair match to the originals. Kits to refoam ripped surrounds, even recone and restore drivers are available as well. these usually come with explicit instructions, or links to sites that offer these instructions, often even videos of the repair process,