I am currently undergoing an integration with the Zend Framework. Unfortunatly we do not use the Symfony framework and have no scope available to include it.
The requirement for sfyaml in its rawest form has caused me to have to rewrite part of your parser to ensure it includes the crrect files which I have now included in our working version of Doctrine.
As Symfony appears to be distributed under an open license surely it would make sense for you to actually include this (or a modified version of this) into your library.
This would make the code much more portable and reusable for people who do not use symfony
My "Quick Fix" just involved dropping all the sfYaml files into the parser folder and doing a straight include untill I can find a more elegant solution