I read about optimizing web player builds and saw something about 10mb being considered large. Also, are files in a project all included in a build or only the ones that are used in scenes?
http://unity3d.com/support/documentation/Manual/Web%20Player%20Streaming.html
This should help if you haven’t read it yet. 563mb sounds like a lot all at once, but if you’re streaming it, it might be okay.