Here is an idea as there are obviously a few of us here using the Amazon Echo. Why not use the Echo Dot in your car? It is powered via USB so that is readily available in the car. And it can connect to your car's speakers via Bluetooth. The one issue is getting a Wifi connection but you could solve that by using your phone as a Wifi hotspot or by having an LTE wifi hotspot. One other issue is Bluetooth conflict as if you connect an Echo then you probably can't have your phone connected at the same time. This could be a better way of having integration, not to mention high quality voice integration, to music services like Spotify, Amazon Prime, etc. Plus you could use other Alexa Skills.