The best thing you can do is put some carpet or a rug on the floor. It's all about the room! I've got a 604 system that rivals many 800 series setups just because I've got a killer room. Listem to your walls and floor; they will tell you what they need.
so you're using the 2 603s as your center channel? this is the first time I've seen someone using 2 speakers for center, does it image better than the LCR600 itself?