I was thinking this as well, but Audyssey should have set them properly, which means if they spec at 60 Hz Audyssey will set them there. I have heard "wispy" as well but I was thinking that could happen if your XO's were set at 120 Hz or so.
I was also thinking it might have been your Denon AVR. In the little research I did there are some complaints about that model, but the wispy sound was not one of them. It sound like you might be getting some sibilance as Schu alluded to further upstream. ^^^