The optical output on the TV is correct. The speakers are then connected to the subwoofer via normal speaker cables. The cable supplied has a cross-section of 0.75mm2 and is already a suitable length for you. I didn't measure my speakers, but according to the instructions they are included in the package:
Five standard speaker cables (gauge 18):
- Two 7.6 metre cables for the rear speakers
- Three 4.6 metre cables for the front and centre speakers.