SR is used to protect the actual recording of the song.....if you wrote and performed yourself, you can use the SR to protect both the recording and the words/music, in essence it acts as a SR and PA all in one......so if someone uses a clip of one of your recordings, they are infringing on your recording....if they record a version of your song or use parts of it in a new song, they are infringing on the song.......form PA covers the words/music only(the song).....
in your first example, you can use SR.....(or PA if you just want to protect the song)
in your second, Im pretty sure you will need PA, unless they will be using a recording made by you......Brad may be able to jump in here and unconfuse me......
what do you mean by "lease"?...Ive heard of selling music, but never leasing.......