iTunes needs a well-formed RSS-feed to populate the podcast. SermonSpeaker 3.4.2 does provide this feed with the following URL:
www.yoursite.org/index.php?option=com_sermonspeaker&view=feed
SermonSpeaker 3.4.2 will also respond to the older format ("...&task=podcast", used with SermonSpeaker 3.3.1) and redirect it to the current one.
If iTunes doesn't update your podcast, then first check if your feed is well formed. You can check this with the W3C Feed Validator.
If it says you feed is not valid, try to figure out why it isn't. This may be caused by bad programmed system plugins or maybe some special chars SermonSpeaker didn't catch.
If the feed validates, we have to check if the iTunes Store has the correct feed URL stored. You can check the underlying feed URL in iTunes after you subscribed to the podcast. Rightclick on the podcast and choose "copy Podcast-URL". This has to be the correct URL of your feed.
If the Feed URL is wrong, you need to change it to the correct one. Now the tricky part begins. The procedure to change an existing podcast feed URL is explained on Apples Podcast page. Basically it means you have to put a 301 redirect up for the wrong URL that points to the correct one. That will only work if you have access to the server the wrong URL points. This may be done with a .htaccess file or a small php file. Either one should work.
If you don't have access to the server or if it points to an invalid URL, you basically need the (2nd level) support from Apple. Or if you don't want to fight with them you can resubmit your podcast and tell them the old one should be deleted. But this will break all existing subscriptions as it's a new podcast with a new ID.
If both your feed is valid and the Feed URL is correct and iTunes is still not updating you may want to open a thread in the SermonSpeaker support forum here and I will look at it closer.