Before you spend any money here's 2 more free ones. Handbrake should be able to do anything you need. Most people think its for video, but it can do audio as well. Its considered one of the better applications if you're looking for good quality. Clementine music player is the other. Its transcoder is very simple to use, but it works surprisingly well.
Both programs work on Mac Windows and Linux.
Both programs work on Mac Windows and Linux.