Clipping is not always audible as clipping does not always occur at the full volume setting. If you have music with a high peak to average power ratio, then a slight increase in power will clip the peaks slightly (i.e., it'll chop off only the tip of the peak). The peaks are far and few in between (hence the high peak-to-average ratio) so you will not readily notice the clipping. If the peak-to-average is higher, then an increase in the volume will result in audible clipping. A good example of the former is soft classical music passages with sudden transients.
The damage to the tweeters occurs when the clipping frequency provides enough power to overheat the tweeters. Tweeters are good for only 5 to 15 percent of the speakers max power handling. Since there's more energy at the lower frequencies, the tweeters never see the full power rating. But, if the amp clips at the lower frequencies and the square wave generates more power than the tweeters can handle, they'll overheat.
Using a low power SET (say 5 Wpc) will most likely not damage speakers rated for 200 Watts max because the clipping from the SET will a) be softer, and b) may not generate more than the 15 watts or so to blow the tweeter. But an SS amp that maxes out at 50 Wpc can probably burn the tweeter of a 350W speaker when over driven.
If you want ear-piercing loud, go with big power amps that are rated at least twice the speaker max power - and bigger if you want to fill a large room. If you want quieter, almost anything will work if you keep the volume control well under the stops.
