Volumio runs really well on a Raspberry pi 3A or 3B.
After a lot of trial and error I have finalised on using a digi HAT with S/PDIF into an external DAC. Another significant influence on sound quality is the power supply that you use. an iFi iPower 2 is a worthwhile investment but you need to keep in mind the power needs of a Raspberry Pi 4 which tends to be more than a Raspberry Pi 3.
Good luck