OK guys. Non-technical person here…so go easy on me. 
Currently running a Raspberry pi 3 with a Justboom DAC and volumio installed on the micro SD card. I use it with Spotify. All is going well…
I have decided to upgrade the hardware to Raspberry pi 4 with a Audiophonics Sabre DAC. Do I simply take the SD card out of the old hardware and insert it into the new gear or do I need to start again with a new card and new flash?
Really appreciate any input…thanks!!
if all goes well you can just transfer the sd card that is in the raspberry pi 3 with volumio on it to the raspberry pi 4, all you have to do is select the correct i2s dac model that you will use on the pi 4 .
do a reboot after switching / selecting i2s dac model.
Thanks very much for the answer!
Just an update for anyone else. In order for the Audiophonics sabre to work you need to download a different version of Volumio onto an sd card for the DAC. This is available on the audiophonics site and you must get the right version for the kit you have bought, in my case the Raspmini LCD. It is now working very well and sound quality is good.