PS. Datasheet of power amps is here
http://inder.cn/WJXZ/nsiway/InderNS4150EN.PDF

It is pretty poor - no mention of what the gain is for these amps. It may be that <0dB is required to achive maximum output which can only be determined by testing.

First time using module I tried ADSL playback and the volume was very low from phone even when volume control was maximum. I compared it to another BT speaker using same driver so volume should be about the same (the comparison was only using VBAT compared with VUSB from Lyra T). Looking at the code...