1. Do not use the 64 bit version. OM was speculating that you were *already* using it and that might be the source of your problem. You are clearly using the 32 bit version. Stay with that version.
2. It's possible that your files have been imported, but the metadata is incorrect or incomplete. To test this, go to Audio > Files . Then drill down into a directory that you know has these AAC files and try to find one. Do you see it? If so, MC imported it. If not, just to be extra sure, type a file name of one of the AAC files in the search box and see if you can locate it that way. If this doesn't work, I'm not sure why your files are not being imported.
3. You probably don't want to use 3, 4, or more libraries. It's unnecessary and it's cumbersome. If you aren't bothered by switching libraries constantly to find your content, then it might be OK for you. Just know that with Views, you really don't need separate libraries at all. It *might* make sense to have a separate low res library for your lossy files, depending up on how you intend to use those files. But for audiobooks and videos, having a separate library doesn't make a lot of sense in most cases. Just import audio, audio books and video into one library and be happy.
Brian.