How many watts per channel are enough?

Higher wattage amps make you feel better about things unless you're an "efficient speaker with a single ended mini watt amp" dude, in which case you feel better when you point that out.

As many as you think you could ever possibly use, then double that.

Consider the fact that often you can save some money by buying the lower powered version of a well regarded design and get the benefit of a greatsounding amp without extra power you likely don't need. Pass Labs makes that point all day. And remember, a tube amp that is pushed in louder musical transients can still sound sweet as the character of the distortion (2nd order) is more ear friendly than a solid state amp clipping, which is a sound nobody should have to endure.

Buy a Lamm M1.2R, that's something serious and you can close that chapter.

Rule of thumb applying the correct amount of RMS power to a loudspeaker. To get the very best performance from a loudspeaker as explained to me twenty years ago by a speaker designer, find out what the maximum RMS power the driver magnets and the crossover capacitors can sustain over the long term of continuous power and divide by two.
If the speaker has a max of 500 watts rms continuous then use a 250 watt amp. There should be at least a 50% volume of continuous current to the magnets. By filling the magnets continuously with current volume at 50% or higher, results in cooler temperatures to the voice coils and crossover network. When you under power a speaker and drive up the volume, you increase the chance of clipping the amp and over heating your drivers causing the coils to fry. If your using a 60 watt tube amp, Match it with a speaker that has a max of 120 watts rms to get outstanding performance. There are a lot of low power full range speakers that are perfectly suited for tube amps.