I have a new N3, upgrading my model from the old Naza M V2.  I use a Graupner tray radio, so I bought a Futaba SBE-1 S-Bus encoder to convert the PWM signals to S-Bus.  The encoder is working well, as I can observe the digital stream from it on my oscilloscope - it's nice and clean.  I can easily see the changes to the stream as I adjust the controls on my Graupner transmitter.  So I know the S-Bus signals going into the N3 are good quality signals.
Connecting my N3 to the Assistant software, the system forced an upgrade of firmware, so it has the most recent firmware.  I have setup the Remote Control settings for S-Bus, but the system doesn't show any recognition of the signals coming into the N3 on the S-Bus port.
Everything else seems to work, but no recognition of the S-Bus.  Is this just a defective unit, or is there something else about implementing S-Bus that is less than obvious?
Any help greatly appreciated!

I have same problem did you solve the problem?

With this S-Bus converter my Graupner GR16 and N3 works.

https://hobbyking.com/de_de/rmilec-high-precision-pwm-ppm-sbus-signal-converter-v2.html