There are some podcast sites that support multiple kinds of files. For example, http://feeds.feedburner.com/BestOfTheLeftPodcast includes both .mp3 files and .m4a files.
It would be a big help if Juice offered a way to download only certain kinds of files. In this case I am interested in only the .mp3 files. Downloading both and then deleting the .m4a files wastes bandwidth and is also a nuisance.