Google Analytics 'Event Tracking' For My Download Links Clicked on Other Websites

Question

I've installed Google Analytics on my website, and I want to now use 'Event tracking' to generate reports on .M4a music files that are contained in my site via typical HTML anchor tags.

Google gives this example of how to do this, which I fully understand:

<a href="../_audio/podcast_024.m4a" onClick="_gaq.push(['_trackEvent', 'Podcasts', 'Download', 'Podcast 024']);">Download</a>

However, in my case, a lot of people are accessing my .m4a podcast files by either:

1) Clicking on a direct link from an external site [eg wwww.music.com/audio/podcast_024.m4a]

or;

2) Collecting the file through a podcast aggregator such as iTunes.

So my question is:

How do I track these kind of events listed above (1 & 2)?

I imagine there is a way to track No.1 by adding perhaps some similar "onLoad" event code? If so, can I group an onLoad event with the current onclick event?

As for No.2, I have no idea?