Prerequisites
Volumio Information
PRETTY_NAME="Raspbian GNU/Linux 10 (buster)"NAME=“Raspbian GNU/Linux”
VERSION_ID=“10”
VERSION=“10 (buster)”
VERSION_CODENAME=buster
ID=raspbian
ID_LIKE=debian
VOLUMIO_BUILD_VERSION=“682e0b17433cee9f9da31457f545345105e06e63”
VOLUMIO_FE_VERSION=“fba46add594d630e1b506bc42f1beddaad53fb64”
VOLUMIO_FE3_VERSION=“c23fef6dba8e02db978bd39bd8d26872e60ada6e”
VOLUMIO_BE_VERSION=“f7885966dee9f148ddf4f5050103a7d6734e1a10”
VOLUMIO_ARCH=“arm”
VOLUMIO_VARIANT=“volumio”
VOLUMIO_TEST=“FALSE”
VOLUMIO_BUILD_DATE=“Mon 20 Dec 2021 04:57:50 PM CET”
VOLUMIO_VERSION=“3.179”
VOLUMIO_HARDWARE=“pi”
VOLUMIO_DEVICENAME=“Raspberry Pi”
VOLUMIO_HASH=“6d5d4c489f0b1e608d9cefb791a9102d”
Volumio Version: Volumio
Hardware: Raspberry 3B
DAC: Hifiberry DAC+
Debug Log
Steps to Reproduce
I upgraded from Volumio 2 to Volumio 3 and noticed a drop in output level play back music files (Flac & WAV)
2.
I created a 0db Sine (440Hz & 1000Hz) test tone file and played it back connecting a pro audio recorder to the output of the DAC. Volume slider at 100% outputs the signal at -32dB. Volume slider (Hardware) behaves erratic - at 0, still sound (lower) playing, jumpy and at 100 the mentioned -32dB
3.
Created a new SD card with Volumio 2 using image file.
PRETTY_NAME=“Raspbian GNU/Linux 8 (jessie)”
NAME=“Raspbian GNU/Linux”
VERSION_ID=“8”
VERSION=“8 (jessie)”
ID=raspbian
ID_LIKE=debian
VOLUMIO_BUILD_VERSION=“dd2a4339faaeb892c7f467e7dc8d424aefb0bd03”
VOLUMIO_FE_VERSION=“958dedc0edff114f244fa9acc70cf53089d9e5ae”
VOLUMIO_BE_VERSION=“fd3e37ffec12db034ec93f94dbc26e5495d5b91a”
VOLUMIO_ARCH=“arm”
VOLUMIO_VARIANT=“volumio”
VOLUMIO_TEST=“FALSE”
VOLUMIO_BUILD_DATE=“Wed Oct 6 12:34:49 CEST 2021”
VOLUMIO_VERSION=“2.917”
VOLUMIO_HARDWARE=“pi”
VOLUMIO_HASH=“98c8f08c531a6f0456f17ab17795e35f”
Running this image on the same system works like a charm - output level for the same file is -12db (20 dB higher than with Volumio 3) volume slider is smooth o=muted, 100 I did not dare as I did not want to ruin my QUAD ESL63s 
powered by a 204 QA class D poweramp (2x60W)
Additional Information
I have a very similar issue on a second system running a JustBoom DAC Zero pHAT (output level far too low) and also on a third system Pi 3 with an IQaudio DigiAmp+