Hey guys, yes; I have plans to add room for multiple manuals, etc. However, keep in mind that you can already add these things to games without much of an issue. You can use additional applications for more than just "applications". It's kind of poorly named.
This will allow you to add an "Open Cluebook" item to any of your games. It's not as easy as manuals, because you have to manually add them, but it should do the job for now.
Per soundtracks, I realize that's a bigger issue. I do want to add that, but it will probably be a while yet.