By grouping your players in the BluOS app, you can have multiple players play the same content simultaneously throughout your home. This is a great feature for when you are entertaining in your home or simply would like to fill multiple rooms with the same music.
To create a group in BluOS, select the house-shaped icon 
in the BluOS app and select the player you would like to act as the primary player of your group.
The primary player is the player whose audio you would like to distribute to your other players. If you are using an external input such as an optical connection from your TV and would like to group that audio to multiple players, you will need to ensure the primary player is the player with this optical connection.
After selecting your primary player, simply tap the "+" icon next to the other players you would like to add to this group and they will begin playing the same audio as your primary player.
While your players are grouped they will have an individual volume slider for each player and also a master volume for all players in the group. To simultaneously adjust the volume on all your grouped players, use the top volume slider for the group. However, if you find one specific player is not at the desired volume you can adjust the volume on that specific player.
To remove a single player from a group you have created, select the 3 dots to the right of the player you would like to remove and select Remove
When you are finished with your group and would like to control all your players individually again, tap the "X" next to your player group to disband the group.
For details regarding fixed groups please see the article below
Creating Fixed Groups.