Well, I am not sure if my input will help as it is not with the Quarto or Model 5, but with the 3A sig. the A23 was not acceptable. I even tried using 2 A23's as mono block in a couple configurations and it sounded better, but far from good. The sound was closed in and dark. I think it was loud enough, but just sounded poor. I upgraded to an A21 and the change was drastically better and I am still using it a couple of years later. I really enjoy my Vandersteen and Parasound A21 combo.
