It's suggested to connect the Bluetooth speaker to your video source device for audio output.
The Bluetooth function of BenQ smart business projectors is built into the Android operating system, which uses hardware separate from other input sources like HDMI or D-Sub. Thus, the Bluetooth function is only available when using the projector’s built-in Android OS or BenQ launcher as the input source. In other words, due to the current hardware design, we can't transmit audio using HDMI or D-Sub to external Bluetooth speakers. If you have any further questions, please contact your local customer care team for more assistance.