I have 2 x Pis connected to the same TV. One Pi runs OSMC out of the box and the second runs a custom CCTV application. Both Pis have the network hard wired (cat5) and connect to the TV via HDMI.
The CCTV Pi does not have any audio input only video feeds from the cameras so there is no sound when the CCTV channel is on.
What I would like to be able to do is have the sound output from Kodi, on OSMC, play through both Pis so that when I have the CCTV channel on the television whatever is playing on Kodi plays as a soundtrack to the CCTV.
Simply cloning the Audio output from Kodi and having that as input to a custom application would be enough as I could code all the other bits to get the feed across the network and into the second Pi.