What is the most demanding on an amp?

woofer always works hardest....tweeters rarely need more than 50 watts max,

there is another factor. some speakers have an impedance that varies with frequency. if an amplifier sees a 1 or 2 ohm load around 10k, it could be a problem.

thus the answer is not obvious. i agree with shadorne, in most cases, but the exceptions could be those hard-to-drive loads in the treble, as mentioned above, especially when a tube amp has to face 1 or 2 ohms.

Hopefully a real expert will chime in, but I think the Magnepan line and 3.6's are a little different. When you biamp a 3.6 you are driving the mid-bass panel and the ribbon with the high frequency amp.

I have read estimates on the planar asylum of a 60/40 power ratio need between the bass/mid-bass+ribbon when driven active. That works out to slightly less than 70% power needed to drive the mid+ribbon than the bass panel. I think the ratios for typical cone speakers would be much less power needed for the tweeter.

One thing does seem to be agreed on... don't underpower the ribbons. Most ribbon failures on MG 3's and 20's are blamed on underpowered amps clipping.

Also, 3.6's are pretty benign on impedance. If I remember correctly, it dips to 3 Ohms at one point, but for all practical purposes they are considered a resistive load.

FWIIW
Jim S.