The powersupply of an amp has everything to do with drive / being able to handle dynamic swings properly etc.
In that sense 1 watt is indeed not the other 1 watt.
1 watt with a large power supply behind it is the way to go in this case .
I would try a set of CAT jl 3 monos on those yg s problem solved i reckon despite being 150 watt or so watts.
Thats if you like tubes off course
I agree that the combination of CAT would be interesting to explore. If they worked on the difficult load of the MBL's, they should work very well on the YG's.