u/gottcha-

For folks who own a JBL Auracast speaker, and also own Marshall Auracast speakers: connecting via bluetooth to the JBL speaker then using it as a Auracast transmitter to Marshall Listen to Broadcast enabled devices works perfect. I'll eventually get a Heddon if it ever goes on sale so I can use Google Cast, but this works fine as well.

Steps

1. Power JBL speaker on and connect via normal bluetooth
2. Start streaming some music to JBL speaker
3. Power Marshall speaker on and connect via bluetooth low energy
4. Open Marshall Bluetooth app and open the speaker's page via the + icon in the top right
5. Click on Listen to Broadcast and select the JBL speaker's broadcast

That's it - the Marshall speaker should sync and start playing the JBL speaker's audio stream via Auracast.

Repeat steps 3-5 if you have additional Marshall speakers.