You can setup the bluetooth as stated below.
I believe Google is upgrading the chromecast to alow it to recieve bluetooth audio.
Amazon echo does now. and is cool as I can pause the PI with my voice.
While Bluetooth is on the Raspberry Pi 3, you need to install a few bits of software to make sure it works properly. It’s best to start by making sure your version of Raspbian Jessie (this won’t work on Wheezy) is up to date. Open the terminal and begin with:
sudo apt-get update
sudo apt-get dist-upgrade
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sudo apt-get update
sudo apt-get dist-upgrade
Follow this up by installing the Raspberry Pi Bluetooth software and the excellent Blueman Bluetooth manager:
sudo apt-get install pi-bluetooth blueman
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sudo apt-get install pi-bluetooth blueman
You may need to reboot after this, but you’ll probably be fine to carry on to the next step.
STEP-02 Set up your Bluetooth speaker
Make sure your Bluetooth speaker is all charged up and ready to go, then switch it on. Ours has a satisfying beep once you do so. If there’s a syncing button or sequence for it to start searching to pair with devices, press it/do it and head back to the Raspberry Pi. If you want to check whether the speaker is actually looking, you could always find out if a mobile phone or tablet is able to see it. Don’t pair with it, though, as that might cause problems in the future.
STEP-03 Connect the speaker up
Open up Blueman by going to the program menu, Preferences, and Bluetooth Manager. As long as the speaker is still trying to sync, clicking Search should make it show up in the interface. Right-click on it, then hit Pair. It should connect to the device, shown by a few information bars on the connection strength – if it then suddenly disconnects straight afterwards, you may need to right-click on it again and hit Connect. Test it out by playing a video on YouTube; it may work straight away like this!
STEP-04 More setup
Depending on how your Pi is set up, the Bluetooth audio might not work at step 3. If this is the case, it’s best to install some extra software to try to get it working. Open up the terminal again and install PulseAudio and its Bluetooth module: