That's the only ruby interface that I'm aware of. The changes needed to make it work with DB XML 2.5 are minimal - have you tried to contact the author of the API to see if he's willing to update it?
Wow - I'm really sorry to hear that. My knowledge of Ruby is non-existent, but if you wanted to take a look at adapting the existing Ruby bindings for DB XML 2.5 I'll give you any help I can. You can email me on first dot last at the obvious domain.