Blubrry PowerPress does not manage existing feeds, it creates a new feed with the framework set in WordPress.
A WordPress blog feed looks like this:
http://example.com/feed/ This feed is XML based, just like the hand written one you have today. It is auto generated by the WordPress platform and out putted in real time. It is not a static file.
In your case,
http://cascadeinsights.com/feed/PowerPress with WordPress adds podcasting to the feed above. In addition, we provide a podcast only feed that looks like this:
http://example.com/feed/podcast/In your case,
http://cascadeinsights.com/feed/podcast/When you edit a blog post, set the Media URL in the "Podcast Episode" box, and save it, WordPress with PowerPress includes that Url to the media file in your main blog feed as an enclosure, looks like <enclosure ... />. In addition, PowerPress includes that blog post in the podcast only feed.
If you want to keep your existing XML file, I have a plugin I can suggest to you. But it does not merge what already exists in the XML file with WordPress, it simply overwrites it. Once you have all 43 episodes into your blog posts in your site though, your podcast only feed will have the same episodes as your static XML file feed so you will not need to do any fancy merging of files. The plugin is called static feed, here is a link:
http://wordpress.org/plugins/staticfeed/Or, instead of using the Static Feed plugin, you can setup a rewrite rule to rewrite your old feed URL to the new one. (I recommend this, much easier to understand what is happening this way)
Another attempt to explainWordPress creates feeds. PowerPress adds additional podcast feed to WordPress to generate with "only episodes". That feed cannot merge data from a static xml feed. Because of this you have to edit each blog post and tell WordPress with the help of PowerPress "Hey this is a podcast episode, here's the URL, now include it in the podcast only feed".
Last Attempt to ExplainFeed (
http://www.cascadeinsights.com/wp-content/uploads/CILife/cilife.xml) hand written
Feed (
http://cascadeinsights.com/feed/) generated by WordPress (blog feed)
Feed (
http://cascadeinsights.com/feed/podcast/) generated by WordPress for PowerPress plugin (podcast feed)
Feed (
http://cascadeinsights.com/feed/podcast/) media must be set by editing each blog post and pasting URL into Media URL box
Feed (
http://cascadeinsights.com/feed/podcast/) cannot merge with feed (
http://www.cascadeinsights.com/wp-content/uploads/CILife/cilife.xml), but you can have feed (
http://cascadeinsights.com/feed/podcast/) overwrite feed (
http://www.cascadeinsights.com/wp-content/uploads/CILife/cilife.xml) using Static Feed (
http://wordpress.org/plugins/staticfeed/) plugin