Let me chime in and explain the problem…
If you are creating podcast content and you only want it to syndicate to select few who know a username and password, then do not use the default podcast channel.
The default podcast channel extends the default podcast functionality that is built into WordPress. What this means is podcast content that uses the default podcast channel can also be found within other parts of your WordPress site, specifically within your main blog’s feed, category feeds (if you use categories) and tag feeds (if you use tags). You can submit any one of these feeds to iTunes. The podcast only feed is optimal to submit to iTunes simply because it does not mix blog posts with the episodes.
In other words, the default podcast cannot be protected because the episodes will also show up in your main blog’s feed, category and tag feeds.
If you want 100% guarantee that only members of your blog can access your podcast feed, then you must use custom podcast channels.
Does that clear up the confusion?