Tube amps that kick ass?

Given those speakers, if I were flying blind, I would try hard to get a demo of some high-powered OTLs, maybe with autoformers (disclosure: no affiliation or ownership history with either). I expect the 450 VTLs would do you fine. I would, however, be wary of using amps at the low end of the recommended amplification range if you want the speakers to come to life.

You might ask what other Vandy 5A owners use for tube amps - you might draw a few out of the woodwork.

Keithmundy,
My Luxman MQ-88 can drive my Verity Fidelio Encores to incredible SPLs in a room that is 15 feet wide, 25 feet deep, with a ceiling height of 8.5 feet. The MQ-88 is a pure class A at 40 watts per side into 8 ohms. In my experience, either that is an overly conservative rating, or those are some of the most robust 40 watts I have ever "heard" . . . !

I heard some Audio Research gear make some truly beautiful music with the Vandy 5's.

Kora Kosmos or Kora Titan Monoblocks

I think of the rock bass you are looking for is actually frequencies above the subwoofers in the 5A, a lot of apparent bass is above 30Hz so you still do need a good tube for rockin bass. The best bass I have heard from a tube amp was the CAT JL2 - though the Atma-sphere with the right speakers does produce really good bass, I don't Vandersteen is the right speaker though.