I'm currently running a 70watt amp with Vandersteen 2ce's listening to classical music and loving it. The Thiel line also works well with classical - may need a little more power.
By no means have I heard all the speakers available and the upstream electonics have effects.
That said,in your budget,for a medium room,of the ones I've heard,I will suggest these two:
Either the Meadowlark Kestrals(89db into 8 ohms) or the Meadowlark Shearwaters(88db into 8 ohms).
I prefer planers to boxes but 60watts is not enough to drive the Magnepan 3.6s.
Funny, I picked up on this thread and I have Meadowlark Shearwaters, the Hot Rod version. They worked fine with my old +/-60 wpc ss amp. In fact, the bass was rather astounding for a two-way, although your room may vary.
Imaging depends a lot on room acoustics but the Shearwaters have the potential to do a great job, in all three dimensions. For orchestral music, I like a good image. For chamber music, timbres and rhythm make the difference to me, and again these speakers do well. Lots of dynamics too.
Where alternative speaker designs may have the edge is in the openness and airiness of the highs. This is not to fault the Shearwaters--they do a great job, but the tweeters are soft domes. Smooth, but not like ribbons, 'stats or Heils.
If you decide later on that tubes are the best way to listen to classical music, the Shearwaters like them. Tubes are what I have now.
Are these to large? http://www.6moons.com/audioreviews/hyperion/938.html
A used pair would fit your budget. This guy has owned many Planer/Stat types and mentions Quad also.
I suggest the Shahinian Obelisk. It is a small footprint floorstander and is closer to the Quad sound than any box speaker I have heard. It also has remarkably deep bass for a speaker of its size (important for large scale classical music). Try www.shahinianacoustics.com Shahinian speakers are famous for reproduction of classical music.