Question on "klipping'?

Clipping occurs when your amp can't provide either sufficient voltage or current to drive your speakers to the desired listening level. A higher impedance load and an amp with lower (internal DC) voltage supply level might tend to run into the voltage limitation whereas a lower impedance load and an amp with higher internal voltage supply might tend to run into current limitation. Obviously, there are many possible combinations. An important consideration is the efficiency of your speaker and the sound levels you are trying to accomplish in your listening environment. When you drive your amp to voltage or current limitation, the clipping or limiting of the output is a sharp tansition in the output waveform which generally generates high frequency transients or "spikes". This is why people with low power amps often blow the tweeters in their speakers and can't understand why. It is usually the amp limitation, not the speaker.

Actually, with balanced push-pull amps (99.9%), clipping occurs in both directions, but that's a minor point. One should also note that speaker impedance varies accross the frequency range, often being lowest in the lower range. Therefore biamping with a higher current capable amp for the bottom end can allow you to keep your sweet tube top end (if that's what you want) with reduced likelihood of clipping problems related to driving a full range speaker with a modest amp. P.S. The power rating often associated with many mid to low fi speakers is not much of an indicator for this concern.