Hi , HiFiBerry is supported on ROCK Pi 4.
HiFiBerry DAC+ Light
HiFiBerry DAC+ Standard(RCA)
To use it, need to update the kernel and rockpi4-dtbo packages. And configure file, /boot/hw_intfc.conf.
Since it is testing stage, we add them on Radxa APT bionic-testing and stretch-testing repositories.
You need to modify file, /etc/apt/sources.list.d/apt-radxa-com.list.
deb http://apt.radxa.com/bionic-testing/ bionic main
deb http://apt.radxa.com/stretch-testing/ stretch main