Oh . . . just saw this. FSA's X-Drive and the nearly-identical On One BMX-splined BB come with a ton of spacers/shims (in addition to the main long center spacer) to get everything dialed. When I find the right link, I'll edit my post.
EDIT - The FSA installation instructions are on a text-only page
http://www.fullspeedahead.com/downlo...stallation.pdf
If you end up getting one of these and want an install guide with picts, PM me and I'll dig up the On One PDF. It was a much clearer guide.