Here`s how to create a stereo pairing with your Amazon Echo speakers
(Android Central)

One of the best perks of owning multiple smart speakers in your home is the ability to link them all together. The Alexa app makes it easy to cast the same music across multiple rooms in your home, but you`re also able to pair two of the same Amazon Echo speakers together to create a stereo pair. What you need to know Stereo pairing is available for the 2nd generation Echo, the 3rd generation Echo, the 3rd generation Echo Dot, the Echo Studio, and both the first gen and 2nd gen Echo Plus. However, note that you can only pair two of the same speakers together. That means your available configurations are two standard Echo speakers, two Echo Dots, etc. Note that both speakers need to be in the same room and within a meter or so of each other for setup and pairing. If you already own a compatible speaker, you just need to buy a second one to complete the pair. Stereo pairing follows the same setup steps as the Amazon Echo Sub, which needs to be paired with one or more standard Echo ...