But then again, it is 8-10 ohms through the entire midrange region and only rises as frequencies enter the overtone region, with two small bass resonance peaks below 100Hz.

I've often wondered what would happen if you took the wires hooked to an 8 ohm HP xover and hooked them to the 8 ohm taps of the tube amp...THEN take a set of 16 ohm LP xover input leads and hook them to the 16 ohm taps...then at high freqs the amp would have the proper load reflected to the plates, as well as at the lower freqs??? Outside the pass band of the respective xovers, wouldn't they be appearing to the output transformer terminals, and the plates, as a really high z...and not be influencing the plate voltage/current(much!).

Personally, rather than force a tube amp to accept a load that varied so much between the LF and HF, I would "throw away" some of the hf efficiency(3dB) by adding a resistor either in series or parallel as needed so its(hf driver) z would match the woofer, then build the appropriate xovers for that desired z with the HF and LF the same. Otherwise, you are GUARANTEED to be causing the TUBE amp to have both "output voltage variations and higher harmonic distortion" in the frequency region being reflected as the wrong z to the output stage. Sam

arggg, gotta run, wife is cranking up "Violent Femmes" in the other room using the McIntosh MC-240 tube amp and 4 Pi's...sounds like I'm missing out on a party:)

I can't recall which cable assemblies you're running, or if yours are different. But the load impedance is pretty easy to find, it's a simple circuit.