I have been using this BT adapter for over a year and the volume has always been sufficient.
In my case, the RCA cinch connections go into a stereo system AUX input (CD, DVD, tuner etc. would also work).
Of course, you still have to adjust the volume on the amplifier.
if you want to go directly to a speaker, these must be active speakers, i.e. with an integrated amplifier ... you can recognise them by the fact that they also have a volume control and require a power supply or batteries