Hi,
Your config appears correct. Few things you could try
- specify codec g711u instead of A, even if you're in Europe
- try the values set the following doc:
http://www.cisco.com/en/US/partner/products/hw/gatecont/ps514/products_administration_guide_chapter09186a00800c4d1e.html
- Limit speed of you fax machines to 9600 or 7200 bps if possible.
I know it is not a consolation, but I have an installation where they hace incompete faxes going from FXS port to PRI. Go figure!
Hope this helps, if so please rate post!