The solution to my booting problem was to follow this post Raspberry Pi 4 8GB - cannot install - "This board requires newer software" - #7 by oXo, where basically you have to:
- Flash a working (or latest) image of Raspberry Pi OS onto your micro sd card.
- Go into the boot partition on the sd card with your file explorer on any computer.
- Copy all the .elf and .dat files you see and save them onto your computer.
- Flash the Volumio image you want to use back onto the micro sd card.
- Replace Volumio’s .elf and .dat files with the ones you saved previously.
The solution to my USB DAC connectivity issues was fixed by using a simple 4 port USB A hub (didn’t need to be powered separately).