It really depends what sort of sound you're looking for. Quad is quite smooth with a strong, warm midrange, with less bass presence than some. Do you want to liven things up? Keep them smooth?
From what I've heard, the Leemas are like Quad - smooth, easy going. This is more of the same, which will more than likely make the combo a little too laid back. We're not fully convinced about QUAD and ATC working that well together, it just seems to lack something. The Dynaudio's will bring a little more bass out of the Quads, if that's what you're looking for. You can try Quad's own speakers, and also the KEF XQ10's, which liven the system up a little, but doesn't change the overall balance too much. Also, the Spendor S3/5r are also worth giving a go, along with ProAc's Tablette 8, which would probably be my favourite.