http://www.stereophile.com/content/vandersteen-2ce-signature-ii-loudspeaker-measurements
I'd say that's a pretty amplifier friendly speaker. The impedance dropping into the deep bass may be helped by a stiff amp though nothing outrageous. I would imagine a number of good small amps would drive it very well such as the Parasound Halo A23. 125W/Ch and good with 4 Ohms.
Based on the measurements, this speaker by the way seems to have an impedance compensation network specifically to make it easy to drive even with modest powered tube amps.