I can disconnect the speakers and hear the volume - and adjust it - through the projector but once connected through the Firestick, the volume is fixed. Have tried two different brands of speakers and have the same issue. Any ideas?
Hmmm. I didn't realize it was a fixed volume control on Bluetooth which is massively annoying. But you're right, I should still be able to adjust the volume at the speaker but I can't, despite trying to different speakers. So here's a thought. If I added a Bluetooth adaptor to the USB outlet of the projector, and connected the speakers via Bluetooth to the projector, would that solve the problem?
First thing to do is pair your phone with the speakers and make sure that the speaker volume control works with that.
If that works then the issue is the way BT works with the stick.
Then you could connect a BT transmitter to the audio output of the projector but not the USB. The projector would not have drivers to let you do that.