The Amazon Echo is an awesome device and Amazon continues to add new feature, abilities, and skills all of the time. The newest one is the ability to output sound to another speaker. The Echo Dot can already do this and if this is your main function, I would recommend purchasing that device because it's only $50. However, if you already have an Echo, in its original tower version, then this should be a neat feature for you.Pairing your Echo to a Bluetooth speaker is really easy:
Put your Bluetooth speaker into pairing mode.
Open up the Alexa app
Settings
Tap your Echo device name
Bluetooth
Pair a New Device
Once your Bluetooth speaker shows up within the app, tap it to connect and wait for Alexa to confirm that pairing is successful.
It would be best to place the Bluetooth speaker at least 3 feet away from the Echo so that there's no interference. "When the Echo device is close to external speakers, it may be more difficult for Alexa to hear the wake word"
-Amazon Product Page