There may be instances where your MOTU AVB will not pass AVB audio correctly. We first suggest you make sure you are correctly connecting all devices according to the AVB Connection Method examples described in our Knowledge Base.
If you're still experiencing issues with AVB audio, make sure to update your MOTU AVB switch to the latest firmware from MOTU to resolve an issue they have noted with their prior firmware which can cause AVB audio to be interrupted or even prevent it from functioning altogether.