FX Return's are NOT available to be sent over AVB Sends. The FX Send is, but because the FX Send is pre-FX Engine, it contains a dry signal. This is by design, to allow external FX / DSP Processors via AVB Send Return structure.
What you can do is say use a Flex Mix and send nothing but the FX to that channel. Then change the AVB send to that flex mix.
So have Flex Mix 16 with just the FX going to it. In digital patching change the on of the AVB channels that you are sending to the Earmix to be that
- So if you are sending your NSB AVB sends 1-8 and 8-16.
- Setup Mix 16 to have just FX sent to it
- Go to Digital Patching, AVB Sends and set AVB 16 as Mix 16