@TomGeorge It's 8 Ohm if I am not mistaken.
I usually only use the first 4 positions of the audio bar shown in the smartphone (it has 15 positions in total not counting with zero).
All I know so far about the board is that it uses a PAM8403 IC (datasheet https://www.diodes.com/assets/Datasheets/PAM8403.pdf) as an audio amp.
I think I could connect VDD to pin 5 forcing it not to mute.
By the way, I'm sorry for answering a decade later.