I think a solution suggested by Tomalak should work universally. Ref: https://stackoverflow.com/questions/3805050/xml-parser-error-entity-not-defined
His solution was to convert character entities to corresponding numerical entities.
You could HTML-parse the text and have it re-escaped with the
respective numeric entities only (like: →  )...
RSS (and Atom) are based on XML, so the issue you are having is that the & in the HTML entities isn't valid.
Typically you can solve this by double encoding the entities so that the & becomes &: &eacute;.
Most RSS readers will then unencode the first encoding, returning it to the original which is then handled by the HTML viewer.