Just a few days ago I had my first SSB QSO with the QMX+. It was from LA to PA - Norway to the Netherlands - on 20 m using a vertical quarter wave antenna.
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 (almost) adequate volume without an amplifier. The speaker is 8 ohms and connected via two 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. Initially I felt no need for any more audio amplification, but after some more use, I see the point in more power output as the audio easily gets distorted when the volume is increased.