Learning Mathematics using only audio.
Solution 1:
I can't really point to a source, but I find the question quite relevant, as audiobooks of mathematic subject can be important also for blind people.
Learnoutloud has a repository of audiobooks and podcast about math and statistics, and related novels as well. Nevertheless it seems to offer no advanced math repository.
PapersOutLoud may be a good project.
Solution 2:
My suggestion would be to narrow down topics you would like to learn and find YouTube videos of them, then download those YouTube videos listen to them during your commute. I have a daily two hour bus commute and use youtube video's audio to reinforce topics i'm learning at school.
For example: Lets say you want to review calculus, listen to this video on repeat for an hour (its 20 minutes long so you could get through it 3 times!) http://www.youtube.com/watch?v=di_bzYD0Mkg
Solution 3:
Try the Lectures Audio Mathematics channel in YouTube. I come across it with the video The Interaction Between Category Theory and Set Theory.