I know forum members are tired of me discussing my system, But lets face it, they are an improbable match on paper. Sterophoile reviewed the 402au and found them to have an output impedance of .22 ohms and and a rise in distortion as the speaker impedance dips below 4ohms. http://www.stereophile.com/solidpoweramps/moscode_402au_power_amplifier/index4.html.
Lets put that toghether with ML CLS. View attachment 276 http://www.stereophile.com/floorloudspeakers/650/index11.html Assigning the CLS an impedance of 4 ohms is being generous. 33 ohms at 1khz, 2.5 ohms at 10khz and 1.9 ohms at 20khz. Sterophile suggests avoiding speakers that dip below 4 ohms.
My listening experience makes them an almost ideal match. I even get excellent bass. Many have called the CLS edgy and and bass shy. One can assume I have no interest in a speaker that sounds that way. Manny ahve suggested that a solid state behemoth is the only way to go. They generally have very low output impedance and the ability to remain stable with complex loads. Such combos have left me cold or tend to be prohibitively expensive. So the question what's going. We can design a near perfect amp based on the parameters we know how to measure. But those devices have usually been found wanting musically. It is why stereo design is part science part art.
Finally I would suggest i would not even consider an SET with he big Wilsons. They must be a good match or why would Steve Bother. I'll be hearing them later this month and evaluate what's going on.
Speaking of solid-state amps, did you ever have a chance to try the Electrocompaniet on the CLSs?
Never heard the combo but someone I knew who had the original Apogees (that dipped to a 1/4 ohm) used that amp years ago and it sounded darn good. (Plus it could handle the load.)