The speaker/microphone is a "For Kenwood" Chinese speaker mic bought for a Baofeng some years ago. I replaced the microphone element with a more sensitive one that I had in my junk box.
Surprisingly, the speaker gives adequate volume without an amplifier. The speaker is 8 ohms and connected via to 33 ohm resistors from the left and right audio outputs of the QMX+. The resistors are the only components in the little square box that the speaker-microphone connects to. I don't feel any need for any audio amplifier.
