I am pleased to say that there is now a valid RSS 2.0 feed available for my blog. Previously there was just the Atom 1.0 feed, since this is format I am using for storage.
I couldn't find any available Atom to RSS conversion utilities, except for atom2rss.xsl from http://atom.geekhood.net/. I had tried using this a while ago, but found it would not produce valid RSS and even corrupted parts of my text through inappropriate handling of escape sequences.
Feeling a bit more confident in my XSLT, I set about addressing these issues. The feed validation service from w3.org now tells me that "this is a valid RSS feed", and so consider this to be good enough for my purposes.
It is slightly disappointing that RSS limits you to a single enclosure (podcast) for each item in a channel, whereas Atom allows for multiple enclosures. Because of this it is not recommended to use the RSS feed since you will actually lose out on some of the mp3 content.
My Atom feed has brought to light some cases that cause a problem with the XSLT code, and there are probably other valid Atom feeds that would not be translated to a valid RSS feed. Nonetheless I feel this is an improvement and am releasing this updated version into the public domain.
I've emailed my fixes over to porneL who originally wrote atom2rss.xsl, and he's kindly updated his site to include my changes.