PixLark,
Great Question. I do not have an answer for you but have you tried soldering any ESCs with motors to the PMB’s M(1-8) = signal, GND = ground, B+ = power?
I interpreted it that you do not need Y-Wire from FMU-PWM-out to these areas because there is a circular signal port M(1-8) on the PM Board. (SOMEONE PLEASE CORRECT ME IF I AM WRONG)
On a separate note, I was wondering how to remap FMU-PWM-out 1-8 and asked here http://discuss.px4.io/t/pixhawk-4-fmu-pwm-out-channel-malfunction-px4-version-1-8-2-standard-airplane/9402 Have you had any luck with this?
Bests,
Jordan