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The simplest method for dealing with excessive volume range in audio controls is to reduce the final audio level to the output jack in ALSA
How to configure the default sound level everytime my device boots?
If you reduce ALSA audio level for Line Out jack to 40-50% you should have distortion-free audio for pavucontrol levels up to 100%
There is a Linux tool that can retask audio jacks so a rear jack can show in GUI controls as Headphone output
Reconfiguring input/output ports - Advanced Linux Sound Architecture - ArchWiki
The alsa-tools package contains the
hdajackretasktool, which can be used (on Intel HDA cards) to reconfigure the sound card input/output ports; for instance, to turn a microphone jack into a headphone jack.
Retask the front headphone jack as ‘Not Connected’ so it cannot create problems for other audio jacks, or be confused with a retasked rear jack
hdajackretask cannot reconfigure amplifier or mixer nodes within the audio device so a retasked jack might not work as well for driving headphones
And the ALSA audio level will probably need to be reduced to allow full level range in pavucontrol