Hello,
there is no standalone version for X64 because all Rebex components can run in both 32-bit and 64-bit mode.
To clarify how it works: Rebex dlls are compiled with "Any CPU" setting so there is only a single set of dlls that support both 32-bit and 64-bit mode. If your application currently runs in 64-bit mode and references or loads Rebex dlls, they will run in 64bit mode as well.
It has been discussed at this forum post.