All that's required is firstly to pair the speaker from the Bluetooth menu: left-click -> "Add Device", then right-click on the Speaker icon to selecting your BT speaker.
@gregeric Have you tried this in conjunction with the Google AIY then? Because mine is connecting to the speaker but still playing through the hardware AIY speaker provided in the kit.
I'm pretty sure it worked in that configuration when I first played with the Voice HAT & AIY (I'm now running it without any google hardware / Voice HAT drivers).
If you're running headless, & you encounter any Bluetooth connectivity issues, you'll find it will revert to the Google hardware for output. The only way to re-enable BT sound is again to right click on the speaker icon & re-select it (you can automate that though with an xdotool mouse-movement script).
@gregeric Just did a quick test. The sound through the browser plays through the bluetooth speaker. The AIY through the supplied speaker. When i detatch the supplied speaker the AIY doesn't make any sound(as expected) even with the bluetooth speaker attatched.
You could replicate my current setup: comment out the dtoverlay=googlevoicehat-soundcard in config.txt, & add drivers only for the mics by following my guide here: viewtopic.php?f=44&t=173640. You only need follow the steps in the first post there, no asound.rc tweaks required.
There are a lot of bits and bobs around the audio.
Run alsamix and see available audio devices.
Do find in files for the strings for those devices.
There could be another dependant config file in your case.
Back up the image and play, play play. That's the fun