It would be a lot easier if speaker manufacturers were more truthful about their speakers. Amplifiers are pretty straight forward, they put out X power with y distortion. But they should also state what power is available when the amp starts clipping. Some amps have circuits to prevent clipping which is great. The problem becomes when speakers are not linear in the power band. A lot of older speakers could barely handle 10% in the very HF of what the speakers could handle in the bass.
Todays speakers are more linear as high frequencies have become more prominent since the use of electronic instruments and synthesizers. So you have to do a lot of reading about the speakers and ask a lot of questions before buying any pair of speakers. If all sounds were more continuous in nature then matching amps to speakers could be easy. But music contains a lot of peaks and valleys in levels and where the peaks and valleys are across the spectrum change, too. Lets take a pair of Snell speakers or B&W, maybe Mcintosh, or Magico. Three of the companies use a single tweeter, Some of Macs speakers use line arrays. So when they say their speakers can handle a 1000 watts, do they mean peak or RMS. Well when Roger was designing speakers it was RMS. But today some of their speaker lit. says RMS and some don't say so you have to assume peak. Whats peak for pop music about 4 times. So if the speaker says 1000 watts they mean 250 concentrated in one particular spectrum or do they mean across the entire spectrum. Well having multiple tweeters the problem is non issue. But how do 40 tweeters match up to just two woofers. Well lets hope the two woofers, do. B&W. Magico and Snell based their specs with power spread over the entire spectrum with the predominance of the energy going to the woofers and midrange but being able to handle at least 25% by the tweeter for shorter periods.
So you take the maximum power handling of the speaker if the manufacturer is honest and that's the size of amp you buy. But you must remember never allow your amp to go into sever distortion. When an amp is pushed to far it can put out many times the energy in high frequencies compromising tweeter and causing them to fail.
In the old days as long as we were only concerned about peaks we could buy amps many times the rating of a speaker. I use to drive AR-3/3a with 130 watts each and never had an issue consistently. Altec drivers and JBL rated at 40 watts were actually rated at less than 20 watts rms but could be driven with 60 watts if the crossover frequency was raised a half octave and the amps never driven into distortion. Klipsch Cornwalls La scales and Klipschorns were rated at 30 watts, but after crossover modifications could handle 100 watts providing no more than 15 watt peaks reached the tweeters. Today the tweeters have a much higher capability. The same goes for B&W. Comparing the 801 from the 70's and the 802 from today the 802 can handle much more power. Magico a relatively recent company and has designed their tweeters to handle more power. But yet the sale rep will always warn you not to buy older used models as the tweeters have a probability of having been compromised.
I have owned amps with Power Guard and with out from Mcintosh. I have owned Crown, Scott, Fisher, and Citation amps with out protection. In 56 years I have only lost one midrange and one super tweeter diaphragm at home. I have never lost or damaged a driver with Mac amps with Power Guard. I always buy amps with a capability of 6 db over the RMS rating of the speaker and some times more. My Woofers are rated at 100 watts RMS. My Crown amps could put out close to 500, my Mac Amps 300. My center and rear speakers were rated at 75 watts they have 240 watts now. The side speakers have 240 though they are rated at at 40. The first thing I did was choosing the correct roll off frequency for each speaker. 50 HZ for the side 40 Hz for the rear , 35 for the center and 25 for the front. This keeps dangerous low frequencies from compromising the woofers. All the amps have Power Guard to prevent distortion from compromising the driver. But one thing Power Guard can't do is correct for you over driving the HT processor or if you use any type of equalization. So you must follow the specs of the pre-amp and amp to make sure they match up properly. Normally this is not an issue with integrated units. If the source is compromised the resulting distortion will reach your speakers no matter what you do. So it wise to use equipment where every thing matches up. Staying with the same manufacturer using the same series of components will relieve a lot of issues.
Knowing something about the history and the design philosophy of manufacturers is important. For instance Mac amps normally put out 30 % more than rated, and some times 100% more peak energy. Crown amps your lucky to get 5 to 10 % more. Mac tube amps don't have the same capability. In fact all tube amps don't have the margins SS amps have. Mis matching the impedance of a speaker with a tube amp is much more of an issue than with a SS amp. Their are some great sounding tube amps out there, but I would want more of a margin, headroom, with a tube amp than I would find necessary with a SS amp. If you like JBL DD series speakers and want to use tube amps, make sure they have 2 ohm taps.