I have the very same problem. Before anyone jumps to a conclusion, here is my setup. B06 plugged into SONOS Play 5 powered speaker with iPhone X streaming directly over Bluetooth. Just switched out the B06 for another brand’s streamer and no problem using normal volume settings… Using the B06 I have to quadruple the normal volume setting to get anything useable. And, yes, my Bluetooth source volume on my phone is turned up to max.
Sound quality is very good, but having to juggle sound settings is very inconvenient and would prevent me from recommending this product.