Optimizing Pro-to-Ultra latency for projector & AirPlay issue with Persistent Groups

I’m looking for some advice on a specific setup involving a WiiM Pro and a WiiM Ultra.

I know this isn’t the standard use-case, but I’m trying to use my WiiM Pro as a wireless bridge (transmitter only, no speakers attached) to send projector audio to my WiiM Ultra, and also as an AirPlay receiver (since the Ultra doesn’t support AirPlay).

I have two questions:

1. Latency Optimization
Since I’m streaming the projector audio from the Pro to the Ultra, I’m trying to get the latency as low as possible to keep lip-sync manageable.
So far, I’ve set “Group Audio Delay” to “Low” and turned off EQ/volume controls. Are there any other settings or tricks I should check to squeeze out better performance?