PowerPoint 2011 for Mac has long been a thorn in my side. If you're looking to add audio to a slide deck and publish into a movie, it doesn't even come close to doing what PowerPoint 2013 for Windows does. Actually, it doesn't even work. You can record audio into it and set timings, but when you save as a movie, the audio just shows up as an image of a speaker and doesn't play. A brief Google search found that this is a pervasive problem - it's not just me. There are rumors of Office 2014 for Mac, but I have found no confirmed release date. There's no guarantee this will be fixed, anyway.
So, I decided to look into Keynote instead and I was really excited because I thought this was the answer to all of my problems but it turns out that Keynote records one big audio file for the whole thing, not separate files for each slide. Darn it. Never mind. What people really like about recording audio into PowerPoint 2013 is being able to easily change a slide here and there without redoing the whole thing. A screencast accomplishes about the same as Keynote. (I was recently reminded that Quicktime on a Mac is also a basic screencasting tool that requires no download - cool!)
My answer to Mac users who want to record audio into PowerPoint for years has been "do you have access to a Windows computer?" It seems that recording audio on the Mac and then exporting on Windows in PPT 2013 retains the audio and timings. I haven't done it much to feel very confident with this fix, but it did just work for me now. If someone wants to do this, I would test just one slide on the two computers the person intends to use, just in case.
Another option is to use a program like VMWare or Parallels to run Windows on a Mac. Back at my old job, I used Parallels and it wasn't great, but that was almost four years ago. I recently got VMWare Fusion and I love it! It is so convenient to have Windows easily accessible on my Mac. I just recorded audio into PowerPoint 2013 on Windows via VMWare and it did work. Windows seemed a little confused about my USB mic and didn't name it properly in the control panel, but it did use the correct mic and I got it to sound great.
I suppose the easiest thing to do as a Mac user who wants the ability to re-record a slide here and there is to add the audio in PPT 2011 and just tell the students how to play it right out of PPT. That's not very elegant though and completely not mobile friendly. I would, minimally, try exporting it on a Windows computer and then put it on YouTube or Kaltura, and then just give the students the PPT file if something goes awry in that process.