The whole "competing for the same receptor" argument really isn't true. It's synergy between compounds that you're looking for. And don't want to stack excess compounds that essentially act the same way.
Just look at large AAS cycles. There may be 4 or 5 compounds. All acting in their own way, along their own pathway (ideally).
So you could run M1-Alpha and Osta together. One would not "cancel" out the other or anything. Just need to make sure they are complimenting your goals. Know that in that stack Ostarine isn't going to add much in the way of mass. It may aid in recovery and pump along with the restorative benefits it provides. The M1A will be your mass builder. Just know what you're going to get out of each.
But I like the idea presented by Burnfire. Run an 8 week Osta cycle into the M1A cycle. If you play your cards right, the Osta can potentially harden you up, lean you out, get things rolling, and have your body in good shape for a quick PH cycle.