Hi quad303,
Doubting Thomas posted some excellent thoughts about the Quads and the M60s. Here are a few further thoughts.
The Quads are electrostatic planar radiators--they use a thin, flat membrane as a diaphragm. Typically, electrostatic panels have limited lateral dispersion, so you have to anchor yourself in the sweet spot to get proper imaging. They do not have impressive bass extension or dynamics in the deep bass and those who want really high playback levels might find electrostatic designs very limiting. If you overdrive electronstatic panels, the consequences are catastrophic--if the membrane touches the polarized grid, it may burn holes in the diaphragm.
Through the midrange the Quads are very neutral and that is certainly the goal of the best dynamic speakers as well. I believe the M60s are very neutral, transparent dynamic speakers. The virtue of dynamic designs like the M60s is that because of its very good horizontal dispersion off-axis, it has an "open" spatial quality that is hard to duplicate in an electrostatic speaker.
On the other hand most electrostatics are dipoles (they radiate to the front and the rear with the latter out of phase) so they may generate a kind of ambient backwave that may enhance the spatial presentation of the speaker. The backwave from a dipole may also be troublesome in terms of room setup.
Regards,
