The cables themselves are quite long:
Cable Length: AC 2m (6.5 ft), DSub 1.8m (6ft), speaker cable (3x 4.6m) (15ft), speaker cable 2x7.62m (25ft)

If you need >8m you can just buy a standard 2 channel cable and extend it manually...

The cables supplied should not be used at all. I find the system top except for the cables, there are very good and cheap twin stranded wires with sheath.

What kind of cable would you have to use exactly? Diameter etc?