Difference in Demands on Amps

Is it possible to get the impedance curves for the 20.1's and 3.6's?

I think there was a thread about a year ago from someone who was having trouble driving the 20.1's with the Cary 500's. If I recall correctly, it was pointed out that the 20.1's had a pretty significant impedance dip to about 2 ohms that you don't have with the 3.6's.
I'd not want to speculate on the 20.7's. The crossovers are different. I'd want to see the impedance curve.

My question didn't come out quite right; what I meant to ask, is there a difference between the load that a 20.1 or 20.7 would put on a set of amps vs. a pair of Magnepan 3.6's? Are the 20's a significantly more demanding load than 3.6's?