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

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

I would argue that Nelson Pass, especially with his First Watt range might be the most inconsistent. He has become the “Baskin Robbins” of amplifier manufacturers with a variety of flavors, some of which seem to change every month.
Some amp manufacturers have offered factory configurable or even user changeable bridging capabilities, taps, topologies, bias options and feedback controls on specific amplifier models.

How would the house sound of Ayre best be described? 

i recall @erik_squires had a very articulate, apt way of describing the ayre house sound... am sure he will chime in...