The advantage of playing thru the stereo is you get better sound quality and use the outdoor speakers.

1. Bluetooth pairing to the Fosi Audio ampliofier. (see below)
Works with most mobile devices.
  - Works to redirect all sound from your mobile device (most are bluetooth enabled).
  - Requires bluetooth pairing first.
  - If a phone is connected thru bluetooth it will disable the chromecast connection.
  - The Fosi Audio amp uses bluetooth 5 which will work all the way out to the fire pit.

2. A chromecast audio interface (see below)
  - Works only with chromecast enabled apps, such as Pandora, Slacker Radio, Spotify, Google Play, iHeartRadio, ...
  which have casting built in.
  - Uses wi-fi for a little better audio

(Apple Music is protected by Digital Rights Management (DRM) and can't be played on other devices without some third party apps to remove DRM.)
Amazon Music only suports casting on android devices, Samsung, Huawei, LG, Motorola Moto, Google Pixel, ....

Here's a schematic of the connections for you techies.

Note: If a phone is connected thru bluetooth it will disable the chromecast connection.

Note: If the volume is too low from the Google Smart speaker you should change it by turning the google speaker volume up ["Hey google set the volume to 100"] rather than turning the volume all the way up on the Fosi Amp.

Note: The volume settings seem to vary depending on the connection.
If it is connected to comecast it can go from 1-100.
If you are playing thru the speaker it goes from 1-10
This seems to be flakey, my home google speaker works differently.
If you ask it to set a higher volume and it is not enabled it will tell you.

• Smart Phone to Stereo or Google Home Mini
  

  Note: If a phone is connected thru bluetooth it will disable the chrome cast connection.

  How to use chromecast:
  It allows you to cast music from your smart phone or the google smart speaker to the stereo over Wi-Fi and play it on the indoor or outdoor speakers.

  Set the Stereo to Aux/Video
  Login to the cabin network mcbridecabin or mcbridecabin-5G.
  The password is on the refrigerator.

  Look for a cast icon in your music app which will ask you where to play the music. The choices at the cabin now are thru the Google Home Mini [Kitchen Mini] or the stereo on the bookshelf [Kitchen Stereo]. Stay tuned for more.

  You will have to balance the volume settings on the app with the volume dial on the stereo. Start with the stereo volume turned down so you don't get an initial blast.

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  Pandora
  

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  Spotify
  

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  Play Music (Google)
  

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  Amazon Music
  
  The chromecast must be registered to your Amazon account, but their instructions (below) are not complete.
  Music Help: Casting Your Amazon Music

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• Bluetooth Connect to stereo.
  
  If your music app e.g. iTunes doesn't support casting you should use bluetooth.

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• Play Google Home Mini thru the stereo
  
  Play music from the Internet on the Google Home Mini or thru the Google Home Mini thru chromecast to stereo Fosi stereo
  . Set the Stereo to Aux/Video
  Say to the Google Home mini something like:

  "Hey Google play some Beethoven on the Kitchen Stereo."
  "Hey Google play NPR on the Kitchen Stereo."