With Bryce 6.1 you can export 16-bit TIFF and PNG formats but you also need Photoshop CS3 to load and modify it. CS2 will load 16-bit but there are only a very few CS2 tools that work with them. Even CS3 doesn't support the whole tool set in 16-bit.
There are some problems with 16-bit PNG export from Bryce  Mac - can't remember about the PC.