Amplifier brand/designer with the most unique and consistent “house sound?”

James Bongiorno for his work with SAE, Dynaco, GAS, Sumo and SST! He designed some of the best SS amps ever: SAE MkIII, Dynaco 400, GAS Ampzilla, Sumo Andromeda and the Nine, SST Ampzilla and the Son! A record spanning four decades! 

Plus he worked on loudspeaker design at Rectilinear in Brooklyn! 

I agree with both Ayre and Pass.  Very consistent sounds, but perhaps for different reasons.

Ayre uses the diamond output stage, Pass deliberately looks for circuits to add euphonic distortion.

After these two, Parasound.

I agree with Ayre. Doesn't Pass have slightly different sound signatures depending on the line? I've read the XA-25 is different from the XA-30.8 which is different from the X150.8 which is different from the X250.8. I found the x150.8 (the only Pass I've herd) to be very enjoyable but not the last word in detail and accuracy.

pass/first watt have more variable sonic signatures across their line than ayre i believe