14. What kind of Bluetooth codec does the M9 support? Why there's no change after changing the codec setting?

A: The M9 supports the Bluetooth codec HWA, LDAC, atpX-HD, aptX and SBC. The HWA will be enabled by default, and if the receiver device supports HWA, then it will be streaming over HWA. But if you don't need HWA, you can turn it off in FiiO Music settings.  

For the other codecs, you can change them in Settings->Audio->Wireless playback quality. Also, please note that the change of setting will not take effect until reconnecting the Bluetooth device.