I am sorry but I don't understand what the problem is, you just need to submit the dynamic url to Google, eg the one that looks something like this:
www.pinturasvillares.es/index.php?option...atid=2,3,4,5&tax;=yes
Google will accept this just the same as the text file, you can vary the URL catid parameter to include different categories. If you use this type of URL then it will automatically update using the current values from the database.
If you are using a SEF extension it is best to configure it so that this URL is not rewritten, this can sometimes cause problems. But actually in your case this does not seem to be a problem. If you click the link you will see that it works.
This approach works, it is how the feed is designed to be used.