The first watts

You are on the right track. Normally and amplifier will be called A/AB, where it will operate in Class A up to about 5-15 wpc then slide into Class AB. The Class A watts will be the first watts used, so they will go first. Power works on a logarithmic scale, meaning that 100 wpc will sound twice as loud as 10 wpc (+3dB).

So if you have inefficient speakers, that are soaking up 100-200+ watts, you will basically be listening in Class AB. Now with average speakers, at normal levels, you may be listening in Class A, and never switch over to AB. Very few amps operate in pure Class A up to 200 wpc, and they are very expensive.

Onhwy61:

Unless you listen at very loud levels, say 85dB or higher, your amp will operate in class A most of the time.

It's partially right. The other part totally depends on speaker. The current demand can be even at lower volume levels especially at crossover points and lower frequencies.

After transition from class A (both transistors conducting) to class B (only one transistor conducting at given moment) it is already linear and class name doesn't make any difference. Actually, increasing bias point to keep it longer in class A would increase distortion (overbias) since it increases area of double gain (gm doubling) caused by the fact two transistors operate instead of one.

I used to have a full class a amp that one could cook a steak on. I didn't feel the marginal benefits were worth the price, weight, and excessive heat.

for the record I'm using Thiel CS 2.4's