We will get the link fixed for the widget settings.
Are you using the default powepress feed for your podcast? (example.com/feed/podcast/) or are you using category podcasting or a podcast channel?
If you are just using the default, you would select Default in the podcast type setting in the widget. Put nothing in the feed slug or category ID.
To get the iTunes button to show up, in your powerpress settings, itunes tab. Put the url to your listing in the iTunes Subscription URL block.
-Mike