D'Agostino vs. Ayre

I would also recomment Ypsilon with Wilson speakers, a very good match comparable to d'Agostino.
I was fortunate enough to have a home demo of a full Ypsilon system on my Thiel CS 3.7 a month ago, i was completely bown away never heard such refinement.
With Alexia's i guess the new Hyperion monoblocks would be the right choice.

Speaking personally... Thanks for the Ypsilon suggestion. They might be Awesome. But I do value long-standing companies or designers, an established dealer network, and will give the tie to products manufactured in the USA. And I am not working on an unlimited budget. I think right now I'm down to a final three. Ayre MX-R Twenties, D'Agostino S-250, or maybe a VTL S-400 II. 

Great great choices of amps for your Alexias. You can hardly go wrong. I stand by my assertion that high powered tubes like VTL  Siegfrieds are preferable with Alexias. The S-400s are adequate but insufficient. The S-250 will outperform anything but expensive high powered glass with your speakers IMHO. 

FWIW I have an S-250 driving a new pair of Wilson Yvettes. Nirvana over at my house. 

High powered tubes are a long shot, for me. I can't afford a pair of Seigfrieds. I've tried to work a deal to purchase a used S-400, but just learned yesterday that the cost to upgrade one to Series II status is $20K.  And from what khrys says, the S-400 might be inadequate. So it will most likely be solid state in my system. The D'Agostino or the Ayres.