You would need the special trainer cord FUTM4405 for use with the 9C. And yes, the 8FG can be the Master for the 9C student.
Also there are indication on the FUTM4405 trainer cord as to the correct way to hook this up. It will be marked which side is for the Master and which side is for the Student.
Please see the 8FG/S manual on page 42 for more information.
Sincerely,
Krysta
Product Development & Support Specialist
Futaba Service Center USA
[email protected]