As Nuance pointed out, I do have five SongTowers and absolutely enjoy them.
Is it overkill? I don't think so, but maybe others would. In the end, who cares what others think?
I have plenty of room and I didn't have to sacrifice any other part of the system to have them, so why not?
I will say that I only went with them once Blu-ray and hi-rez really started to happen. Having five of the exact same speaker allows one to really maximize a HT setup and fully take advantage of Blu-ray and its lossless, hi-rez capabilities. It isn't like the old days when there was matrix or mono sound in the rears...today's Blu-ray discs are finally fully exercising and making use of the rear channels.
Anyway, I say go for it...I know I have no regrets on going down this path.
George