How do I group multiple A1-MRs together?

Once you have set up all of your A1-MRs on your Wi-Fi network:

Open the Audioengine control app. Swipe from right to left in the app to the "Device" screen where your A1-MRs are listed. Determine which group of  A1-MRs you want to be your primary, then touch the "+" in the upper right corner. A list of any additional A1-MRs you want to add will appear and you can tap the empty circle to add a check to the bubble, then tap "Done" You can add multiple A1-MRs into that primary A1-MR for whole-home playback.