FYI, when you purchase digital music through iTunes/Amazon/etc, you still don't actually own anything. You are purchasing a license for personal use, which can be revoked for various reasons.
In practice I doubt this would ever be an issue, but just wanted to point out that you effectively never "own" a digital reproduction of something unless you are the actual copyright holder (or the copyright is permissive), and digital copies can be clawed back in a way that a CD or physical book you purchased cannot.
Of course if I broadcast it publicly or share it on bittorrent I am in violation. But if all I do is keep it in my music library for myself to listen to, it’s OK.
So, while the MP3 is covered by an Amazon license and the ripped CD has an implied fair-use license, those license terms are more-or-less the same.