http://sound.westhost.com/project35.htm - This website explain how to create a DI box, and some of the principle of converting an unbalanced signal to a balanced one. However I need to convert a balanced signal to an unbalanced input (unfortunatly).
http://www.rane.com/note110.html - Notes about ground loops and audio conections
http://www.dplay.com/dv/balance/balance.html - more about balanced wiring.
http://www.suite101.com/content/wire-a-balanced-microphone-to-unbalanced-inputs-a64018 - possible solution