Yes, speakers measured with calibrated microphone. Interconnects measured with DMM. I agree that impedance is not the only thing which make a tube amp sound different, but it is what contributes to a majority of the sound. Tube amps also sound "warm", because of the higher distortion. Distortion actually makes things sound "warmer", whereas very low distortion sounds more "clinical". Hence the terms some use when describing SS and tube equipment.

It might not be just the output impedance, but in my experience, 1000 ohms such as in the 990 is very high! 100 ohms is much better! In fact 1000 ohms o/p impedance is the highest I have seen on SS gear. The testing was done in both stereo modes, and the "veiling" was there in both modes. It could have something to do with something else in the circuit, but I do not a have a schematic to make any conjectures.

Tim