Dave
The weak sound is likely due to the volumeicon app only working with the master channel but the preamp channel still has an active value.
For separation between speaker and headphones… this is probably due to antiX using alsa and Mint using pulse audio.
I think it is possible to separate them in alsa as well. I have not idea how though.
Computers are like air conditioners. They work fine until you start opening Windows. ~Author Unknown