[vasilis]

Eventually, I solved the issue by doing two extra things:
- I removed any mod_rewrite rules in the .htaccess file of the WordPress root directory, because they broke the initial redirection
- I tried to remove my code tweak posted in this thread, but then the site displayed the database connection error, so I retrieved it back.
- I deactivated the W3 Total Cache plugin in WordPress, because it kept breaking the site (as skot suggested in this post).

The strange thing is that I needed to keep my code tweak as well.
Anyway, the integration worked fine.