I have an eshopps M overflow on a 40B quarantine tank. It was the first time I drilled a tank and a great kit that came with the diamond hole saw and template. It's being fed by an Eflux 1050 GPH pump through 3/4" PVC and dumping into a 20G long with homemade baffles (copied Fiji Cube design). I was shooting for silent operation and had noise from from overflow like you describe. While coarse foam can maybe silence or mitigate the noise, it can also clog and ruin your day.....
I tried something a little different and can speak of it with a year of successful operation now. My return line has a nice gate valve for fine adjustment, but I just couldn't find the "happy spot" with regard to noise due to turbulence in the overflow itself. So I "throttled" the wet side of the overflow by blocking (in this instance) 5 of the weir slots. The system went silent and after a year of use the material I used to block them might be of interest. I used Flex-Tape. I looked for any reason not to prior to trying it and didn't find anything negative. The tank is as healthy as Eden and the coralline forms on it at the same rate as the acrylic and glass making me think this stuff is inert with regard to its chemistry.
Cool product and might be really handy in emergency leaks.
The emergency drain faces straight down at 1/2" above sump level to minimize splash but make some noise, and the return dumps into a single 4" sock about 1/2" below sump level for silence.