I am successfully using Atma-Sphere MA-1 amps with the Vandy 5A's and it is a wonderful combination. It has a rich midrange with tons of detail and texture, airy highs which float and decay a spooky realistic way, and bass that has authority, depth, and definition. All of this while producing a sound stage that is very deep and wide.
Putting all that praise aside, the most important aspect to me is that the Atma-Sphere/Vandersteen combination does an incredible job of drawing me into the music and allowing me to make an emotional connection to the music that other amps simply can't do. This translates into me wanting to listen more often and for longer periods of time.
I have tried amps from McCormack, Pass, Meridian, Sunfire, Moscode, Jeff Rowland, VAC, Cary, Rogue, Dodd, and many others and none have given me the level of enjoyment that the Atma-Sphere amps do - highly recommended.
George