To transfer music from a Mac to a stereo system, you can use the FiiO BTA30 Pro as a Bluetooth transceiver. The BTA30 Pro can send digital audio input to other devices via Bluetooth. You can connect it to your Mac by operating the BTA30 Pro in Bluetooth transmitter mode and connecting it to your stereo system that can receive Bluetooth. Alternatively, you can use the BTA30 Pro as a DAC to convert the Mac's digital audio output to an analogue signal, which is then sent to the stereo system.