Pass Labs XA30.8: is it enough for Wilson Sasha 2?

I'm surprised by your statement, probably is not the Symphonic Line at fault here but the speakers-room interaction???

Not enough power look at Pass 250.8 or keep on trucking!!!

I have the Sasha 2 powered by the ARC Reference 75 SE which is more than adequate. Prior to my purchase I did a fair amount of research, and on two sites it was reported that Wilson used the Ref 75 to voice the Sasha 2 s. 
My dealer had the Sashas setup in the  showroom with the Ref 75 SE for demo purposes and he knows his stuff owning the same store since 1977. He did hook them up with the Ayre mono blocks which also sounded quite good ( a lot more money ), but to my ears I preferred the ARC.
My listening room is 21x15.

Well, my (dedicated) room is very small 3.45m x 3.25m. Displacements of furniture, loudspeakers and listening point is symmetric. I have also placed two tube traps to control better bass response. I’m going to add some adsorption (behind loudspeakers) and diffusion (behind listening point) panels.

I can add that I tried also another amplification chain: ARC LS5 + 2 ARC Reference 250SE. Well, the sound gains in sweetness, is less strenuous, maybe more recommend for classical music; but it loses a bit in soundstage and in the bass control.
I still prefer the Kraftwerk (and also my friends) for jazz, r&b and rock. Sound has more dynamic, it is fuller, transients are excellent, even if it is more tiring in the middle and highs.

Some news. First of all, I’ve to apologize for a big mistake: in all my previous post, the pre is not the ARC LS5, but the LS2. I don’t way I was convinced that it was this model... maybe I was without my glasses in my first approach!

Second, waiting for a test of a new power amp, I had the opportunity to test the ARC LS25 mkII with the Kraftwerk.
The result is better for soundstage and details in the mid range, very clean.
But it is worse for bass range, very poor, and highs, a bit more harsh. Overall a sound more tiresome. For my taste, a chain one step behind.