Audio works well on Raspberry Pi OS and Ubuntu, both using pipewire.
Audio works on DietPi, which does not have pipewire.
It seems that the device that was selected at the time SparkSDR is started is the only one that works.
To switch audio devices, select another device and restart SparkSDR to use that device.
When switching audio devices back and forth, sometimes a device will disappear from the list.
Virtual audio cables do not appear as a selection.
I also noticed that FM has audio compression. When there is a few seconds of silence, I can hear the background noise increase dramatically.
There are no AGC controls available on FM.
This is not what an audiophile would want with music.