I haven't heard this speaker but am a fan of most of their design principles. It seems Vandersteen recommends bi-wiring a pair of stereo amps in for the very best results. The specified efficiency is 85 dB/w/m at 2.83 volts and recommends 40-200 watts at 8 ohms. Impedence is stated to be 6 ohms, 4 ohm minimum, but an "easy" load (as expected for an all 1st order crossover design). They recommend a stable (low impedance friendly - read solid state) amplifier design and keeping speaker cabling as short as possible.
So the goal would seem to be a pair of 200 wpc solid state stereo amps. Around Audio Circle Digital Amplifier Company's stereo maraschino comes close (125 wpc, $2400/pair); NuPrime STA-9 works (120 wpc, $1390/pair); and Odyssey Khartago works (110 wpc, $1990/pair. PS Audio S300 could come close (140 wpc, $2998/pair minus trade-in). Keep in mind that the difference between 40 and 200 watts is 7 dB of gain and the difference between any of the above amps and 200 watts is less than 3 dB (half again as loud). Depending on your room size any of these amps could bring you near symphonic peak volume levels.
If you want cheap, look at the Crown XLS 1502 (300 wpc, $878/pair). They sound great for the money (fan rarely comes on), but IMO a poor match quality wise to the Tree CT.