If I understand it correctly, L9R does not allow any changes to the assignments of channels to the connectors. ch 1-9 are fixed to conventional pins and ch 1-12 are on the single sbus. You could:
A) connect additional devices listening to ch 9-12 on the same Sbus together with your APM 2.6
B) check APM 2.6 if its channel range could be changed to ch 5-12 instead. The same could be don on the Taranis in order to free up ch1-4 for additional devices on the conventional pins of the L9R
