One reason I went with the 4's was the ability to upgrade them by adding the midhorns and theater 7 crossovers, which I did this weekend. I'll preface these comments by saying that I don't have usable corners and my midhorns are a worst case scenerio, slapped together in a few hours as a test, with a leaky .7 cu ft box containing (sort of) the driver and plopped down on top of the 4's. I haven't had a chance to do a lot of listening yet but these are my initial impressions...

On average rock blues etc. recordings the midrange is cleaner and more detailed and the bass seems a little cleaner. On several songs I've noticed backing vocals and instrumental lines that I really hadn't heard or paid attention to before. You seem to hear more of the music without the hyper detail that makes many of these recordings hard to listen to. But on well recorded music the midhorns really blew me away. They do a wonderful job of reproducing a sense of space and scale, making my back wall seem to disappear completely. I can't wait to listen to my favorites.