I currently have an MX-500 and a MX-350 that operate five Sat receivers (Bell) each.

You need to do the do these one at a time. To save a lot of grief unplug the sats that you are not programming. To change the sat remote address use the original remote. LABEL each of your sats as Remote Address 1, Remote Address 2 and Remote Address 3.

Take the original remote and turn on the sat. Press and hold the SAT button on the remote till all lights flash. press the 2 button then the # button.

Voila that sat is now programmed as remote #2. Now learn the MX from the original. Then do sat three.

Good luck!!!