Chris, try http://www.beoworld.org/prod_details.asp?pid=411 ; otherwise select products and then select 'User & Service Manuals' at the top right of screen. Choose 'Music Systems' then 'BeoCenter Music Centers' and 'BeoCenter 9300' and 'View Manuals'. There should be at least the user manuals there.
Cabling pinouts for PowerLink are:
Pin 1: PowerLink on >= 2.5V; off <= 0,5V
Pin 2: Signal Ground
Pin 3: Audio Left out: 0V--6.5V RMS
Pin 4: PowerLink Speaker on >= 2.5V; off <= 0,5V
Pin 5: Audio Right out: 0V--6.5V RMS
Pin 6: Data High >3.5V; Low <0.8V
Pin 7: Data Ground
Pin 8: No connection
No connection to metal jacket
Good luck!