A change in efficiency to the final sound

jrwaudio ;
   I would be interested in what you find out there . 

Now if I could hear from someone that has done it the other way two different speakers on the same amp , that would complete my information quest !

Thank you .

I don’t believe that the VAC amplifier switches between SET and push pull (PP) operation. Rather it switches between PP triode versus PP ultra linear output. This particular VAC amplifier  is a class AB circuit. SET amplifiers are by default pure class A exclusively. Technically speaking the KT 88 if used to run single ended would be a SEP class A (single ended pentode) as opposed to SET (single ended triode) which are DHT (directly heated triode). Such as 300b,2A3, 845,, 211 etc.
Charles

"...I forgot , in the post that you responded to , to add that the volume levels would be adjusted to be the same for both speaker tests .

Does that change your thinking ?"

What I stated was how the efficiency values are interpreted. If you compensate for the efficiency by increasing the volume, then you're basically asking the amplifier to work "harder" which in case of most tube amplifiers, particularly low powered SET designs, means more distortion. Aside from the speaker efficiency, another important criteria is the speaker's impedance and how it varies as a function of the frequency. Typically, the higher the impedance the less demand from the partnering amplifier which also translates to less distortion. 

@saki70 it might be awhile before I get my Magnapan 0.7's More than likely another 6 weeks : (   But I will post my findings for what it's worth : )  I found this on my VAC PA 80 80 manual, I had to sent it in and the UPS guy might of been mad at me as it weighs over 70 lbs
They also did an over all upgrade caps etc
It still has the original KT 88 Golden Dragon Tubes

Ultra-linear or Triode?
The input amplifier, phase splitter, and driver stages are triode tubes operated in ClassA with no cut-off or grid current. The output stage is connected for partial-triode, well known for low distortion, good damping factor, and high efficiency. This technique was invented by Alan Blumlein of EMI in England, and was popularized in the US as "ultra-linear." VAC can convert amplifiers to triode connection for a small charge.

Yes the input stage is class A as are nearly all input /preamplifier sections in amplifiers (power or integrated). I was referencing the  KT 88 "output stage" which is class AB. Pentodes can be wired to function in triode mode.
Charles