HELP CENTER 
How do I play SiriusXM on multiple Alexa devices simultaneously?
How do I play SiriusXM on multiple Alexa devices simultaneously?
  1. Associate all Alexa devices to the same Amazon account (contact Amazon for assistance with this).
  2. In the Alexa app, select the Devices icon (5th icon at the bottom menu).
  3. Click the plus (+) sign (top right corner) and select Add Group.
  4. Type in or select a Group Name. Press Next.
  5. Select the devices you want to group. Press Save.
  6. Say, “Alexa, play [channel name or number] on SiriusXM in the [group name].”

NOTE: You can only stream one SiriusXM account to one Alexa or Alexa group at a time.