I think I figured out I need a receiver connected to the sound bar system. I’m not sure why Bluetooth alone isn’t enough for the Vizio 5.1 I have, because Alexa can connect just fine to JBL Bluetooth portable speakers. I’ve looked into the Bose wifi audio system as a solution and it still has to be connected to a receiver. Without smartcast, Vizio won’t connect. My iPhone connects perfectly to the sound bar and Alexa, I just lose audio on Alexa with the 3.5mm aux. I’ve seen this reported in several reviews about the Echo Plud. Maybe they will do an update to fix the issue or Vizio will offer an adapter. Thanks for the suggestions!