If you are going to use a second pair of Quads, try positioning the outside pair perpendicular to the inside pair. They should be positioned so that the outside pair fires outward at a ninety degree angle relative to the inside pair.
Start so the middle of the outside speakers are at the middle of the outside edge of the inside speaker.
You then move it slightly forward or backward till the image locks in.
You still wire the speakers on series. This should give you the benefits you already have, but the sound stage should open up dramatically, with an attendant dramatic improvement in air and space.
This positioning method was first used by Alastair Robertson-Aikman the founder of SME with a pair of 63's.
Pierre Sprey of Mapleshade is the one who turned me on to this. It is now, in some quarters, the preferred method of using two pairs of any type of electrostatic speaker, although, it should work for any type of dipole speaker.
