First of all, congrats on your Quad purchase! I haven't heard the new models, but I've owned several pairs of Quads over the years, and like the new braced frame concept.
Distance to sidewalls is not critical with large panel dipoles, though generally you want them far enough apart to get good soundstage width.
Distance from the backwall is much more of an issue. You see, ideally you'd like to avoid a strong reflection arriving within say 10 milliseconds of the first-arrival sound. Three feet out will give you roughly 6 milliseconds delay before the reflected backwave reaches the listener. So I would recommend diffusion (not absorption) panels behind the speakers, offset towards the centerline of the room a bit, to intercept and diffuse that first reflection backwave energy at least in the midrange and upper frequencies.
In the bass region, dipoles behave very differently from monopoles. You see, its the out-of-phase backwave that will be getting the benefit of boundary reinforcement off the nearby "front" wall. So moving them close to the wall will result in greater cancellation of the frontwave, and actually decrease the bass at the listening position. If too much bass is lost, you might try putting a couple of bass traps in the corners behind the speakers, as this will help to soak up some of that out-of-phase backwave energy so that there will be less cancellation of the frontwave.
Best of luck to you,
Duke
Distance to sidewalls is not critical with large panel dipoles, though generally you want them far enough apart to get good soundstage width.
Distance from the backwall is much more of an issue. You see, ideally you'd like to avoid a strong reflection arriving within say 10 milliseconds of the first-arrival sound. Three feet out will give you roughly 6 milliseconds delay before the reflected backwave reaches the listener. So I would recommend diffusion (not absorption) panels behind the speakers, offset towards the centerline of the room a bit, to intercept and diffuse that first reflection backwave energy at least in the midrange and upper frequencies.
In the bass region, dipoles behave very differently from monopoles. You see, its the out-of-phase backwave that will be getting the benefit of boundary reinforcement off the nearby "front" wall. So moving them close to the wall will result in greater cancellation of the frontwave, and actually decrease the bass at the listening position. If too much bass is lost, you might try putting a couple of bass traps in the corners behind the speakers, as this will help to soak up some of that out-of-phase backwave energy so that there will be less cancellation of the frontwave.
Best of luck to you,
Duke