First time user of this brand. Manual says it can be configured with sum signal? I assume a Spektrum SRXL connection should work. This would get fid of the piggy back jumpers and the servos can be plugged into Cortex? Are the remaining slots on Cortex usable for other channels/ servos? Any input is appreciated. Thanks

Um...what?

I believe the Standard will only take Serial (SBUS, etc.) in, with PWM out (must use the wire loom). The Pro on the other hand will do SBUS in & SBUS out.

Srxl is not compatible with Either Cortex. You will have to use the wire loom.