A single Myo armband can be paired with multiple devices and more than one Myo can be connected to a single device at a time however, a single Myo armband can only communicate and control one device at a time. A single Myo armband cannot control multiple devices at the same time. To switch between devices, you must first disconnect Myo and then connect it to the new compatible device via Bluetooth.
The maximum number of Myo armbands connected to Myo Connect via the USB Bluetooth adapter is 3. Myo Connect currently only supports 1 USB Bluetooth adapter connected at a time. Developers can use the Bluetooth Protocol to create their own connection and have more than 3 Myo armbands connected however, packet loss will occur without the use of a secondary Bluetooth adapter.