Best amp to drive Wilson Yvette’s

OP:
I find the Luxman and Ayre have a very different sound than the Pass, especially in the bass.

Really suggest you listen though, my opinions here are not shared by many.

I would second the Vitus if you can find one used. The best I have ever heard Wilsons sound was with tubes, but the system ran out of gas very quickly due to the low power of the Lamm amp in the system. Low level detail was exceptional on this system.

Audiovalve makes some higher powered tube amps that are really good. 

Surprised you'd think you need more headroom over what the Pass 250.8 can deliver.  It puts out 250 watts per channel into an 8 ohm load, which doubles to 500 watts per channel into 4 ohms. In stereo, the Luxman m900u by comparison delivers 300Wpc into 4 ohms continuously, although dipping down into 2 ohms the Luxman likely delivers more power than the Pass - but is that really helpful?

I'd vote ARC Ref 75SE as well. Gem of an amp and (relatively) inexpensive 

Maybe I'm totally missing something but how does the ARC Ref 75SE provide the OP with more headroom for the Wilsons than he is currently getting from his Pass 250.8?