If you are using Resolve, you are stuck with BMD gear for i/o. There will always be latency with their devices when the a/v path is going through 2 separate units. I have separate audio and video i/o and have found that it’s a crapshoot with Resolve. Sometimes you push play and it’s dead-on, then the next time it isn’t.
With BMD your only choices are the UltraStudio 4K products, but I don’t see where they support 5.1. Maybe via HDMI output? Or maybe something in tandem with their Fairlight hardware. But the BMD website largely buries the Fairlight hardware, so I don’t know the answer to that.
I would suggest going the ProTools or Logic Pro X mastering route if you want to do it right with your client.
– Oliver
Oliver Peters – oliverpeters.com