There is value in using both PowerPress and FeedBurner, FeedBurner will give you feed usage statistics while PowerPress will build all your media URLs and format your itunes tags appropriately. I suspect the main problem is your FeedBurner settings are pulling in your main RSS feed from your blog, not the podcast only feed which is why all the mp3s have gone missing. Simply go into your Feed Settings page (in advanced mode) and in the first option select 'Enhance all feeds'. then click save. This will enhance (add itunes and podcast tags) to your main RSS feed.