According to the AP21-22 Installation Manual:
4.8 Cable connections
Use only shielded cables. This includes Mains input, drive units
and if necessary for the extension of the RF300 Rudder Feedback
cable. The clutch/bypass cable and the solenoid cable should be
1,5 mm2 (AWG14). Signal cables should be 0.5 mm2 (AWG20)
If I were going to extend the control cables, I would call Simrad for some bulk cable or check eBay for a length of used Robnet cable long enough to make your extensions. The twisted pairs are important and the shielding is even more important. I'm sure good mechanical or soldered connections will be just fine, but make sure you also splice the shielding and insulate it well.
As it turns out, I am re-routing some Robnet cabling on my boat and may have some I can send you. PM me so we can discuss.