I'm currently importing my PSN games to LB, and it's exactly like explained in the posts above, install the game inside RPCS3, drag and drop the EBOOT.BIN file into LB and off you go, just remember in the last step to rename your EBOOT file, otherwise LB won't recognize it.
Files are in emulators\ps3\dev_hdd0\game (for PSN) \disc for disc games.
Use aldotools PS3 Game Updates to easily find the latest update files for all your games, only might have to also get a newer .rap file.