There would be no sprinkler timer or to put it another way, the XOVR and/or M1RB replace the sprinkler timer. I am not that familiar with Elk but it looks like there is a 4 wire data bus that would be run from the M1 to the XOVR/M1RB to connect them. The XOVR/M1RB could go where the sprinkler timer would go, remote from the M1, or it could be in the same location.