Which amp for Vandersteen 3As?

I would recommend trying out the McCormack amps. I used a DNA-1 with 2ce Sigs. I corresponded with Steve McCormack on a few items. He used Vandersteen 3's in his personal system. He may have voiced his amps with them, not sure. I second the value of having the designer continuing to support the amps with questions, service and upgrades. He is very helpful. Good luck.

Vandy's are not a difficult load for most amps.
McCormack is a good choice.
Belles is also highly recommended.
If you want the best, then Ayre is the way to go.
I only post this because I tried them all.
One thing I will point out is that Vandy's seem to work best with Zero Feedback amps.
Bob

I've driven my 3A Sigs with a Krell KAV300i integrated, a Musical Fidelity 308 integrated, a Pass Labs Aleph 3, Audio Research VT200 and Ref 110 (currently).

The Aleph 3 was not powerful enough to really drive them in my larger room. The others were all good with the two 150w SS amps having better bass slam than the tubed ARCs. 

I've added subs and a crossover and now feed the ARC Ref110 a signal crossed over at 100Hz. This combo is the best of all of them.

Even before adding subs I found both ARC amps had plenty of bass extension and slam for me.