Originally Posted by jautor
Yep, you got it! The only real downside to the "all Chromecast" setup is that you are limited by whatever you can get to the Chromecast. So simple analog sources like an FM tuner or TV / set-top box audio aren't available to the WHA system. This was important to me as I use the WHA system to listen to the news in the morning (from a set-top box), and it's also good for the game room zone during sporting events.
The higher-end systems from Sonos, Russound, NuVo, etc. all have 'line input' capabilities on the zone streamers to allow for this.
So I think that we should be very clear on this point when it comes to Chromecast. Jeff has rightly stated that Chromecast doesn't have the 'line input' so that you can stream your tv set-top box audio using the 'line output' on the back of your set-top box to the WHA speakers.
However, casting a tv channel's audio to a Chromecast Audio device can be done without having the 'line-out/input' connection using the Background Audio feature that is built into Chromecast. Most multi-channel providers that provide customers with a set-top box also have a complimentary app that users can use to stream live tv and dvr material. Directv, Dish, Xfinity (Comcast), Charter, and others offer a complimentary streaming app for their set-top box users.
You can use Chromecast's Background Audio feature to cast audio from any app to your Chromecasts. This means that if you want to stream audio from a tv channel that is available on your multi-channel provider's app you can do it. I have Directv and their Genie and mini-Genie clients as my set-top boxes. But I also have the Directv app that allows me to stream live tv from all of the channels including my local channels no matter where I am. In the past 10 months or so I've streamed live tv audio from the Directv app throughout the speakers in my WHA system for college football, NCAA basketball tournament, and NBA playoff games using the Background Audio feature of Chromecast.
In addition streaming apps are also available from the likes of Netflix, Hulu, Directv Now, Dish Sling, Playstation Vue, CBS and so forth, where the app's audio can be cast to a Chromecast Audio using the background audio feature. Directv Now, Netflix and CBS Sports have the Chromecast casting feature built into the app.
The number of people streaming tv shows using an app continues to grow and multi-channel providers that offer an streaming app as a compliment to your traditional set-top box is large. The future is clearly streaming tv shows through an app and some people are/have moved in that direction. As such the lack of a 'line-input' becomes less of an 'issue' when you have a streaming app available and you're using a streamer that doesn't off a 'line-input/output'.
BTW, if your local FM or AM station has an app (most are on I-Heart or Tune-In) you can cast that app's audio to your Chromecasts using the Background Audio feature. The feature is not limited to a specific type of audio or app. Any app's audio can be cast. So if you want to cast that local FM station that isn't available on the Tune-In app you can use Background Audio.