Short clear cut answer to "Do I have to own the Audio I post?":
Long, possibly, maybe confusing answer:
This is not a file sharing site, and it is against the rules to upload anything that you did not create (Especially copyrighted material). You cannot upload your friends music, you cannot upload your favorite bands music, you cannot upload another song submitted under the Creative Commons license. You can upload remixes (Of things uploaded under the same license, I.E. Creative Comments) or remakes/covers, but you cannot upload anything that you did not in some way contribute to, regardless of whether or not it was uploaded under a Creative Commons license.
Questions, Comments, Concerns, Mass Confusion?