I have the att bgw-320 as well. Very excited for when the hardware for the bypass comes around.
I tried using the IP passthrough setup on it, but it ended up causing all sorts of slowdowns that I had troubles diagnosing. I was using the nanopi r4s with a WiFi AP when I had this issue. Make sure to look into compatibility with ATTs IP passthrough is not total passthrough so you might have to dig into the details to make sure it all works together.