My point about conjugating the imaginary (reactive) impedance of the cart is to cancel out any inductive or capacitive reactance so the cart sees a purely resistive load which will give the flatest frequency response with no peaking at high frequencies.
Flattest frequency response or best square wave ? Are these codependent ?
With Jensen SUT's that are designed to be used with a zobel network they suggest adjusting the network to the source load by scoping a square wave.