James, The best description I have heard of the difference between DSP5000's and DSP5500's is that the bigger speakers have more "scale". I have DSP5k's and am really impressed by how good they are - clear, detailed, transparent and they can go deep too. I've listened to DSP55k's and they are wonderful - they do all that the smaller ones do with that extra scale of height, depth and presence. Do you plan to stop at a stereo pair? If so I'd go for the DSP55k's. If you want surround, and budget or space are an issue, a room full of DSP5k's might do better.

Steve