This is the implementation of what is explained at https://wiki.archlinux.org/index.php/PulseAudio/Examples#The_shell_script_method with specific improvment related to the Behringer UMC404HD interface.
Everything there has been tested on UbuntuStudio 21.04 with the 4 inputs and Roland RD-88 added as analogic sound source + midi interface.
You must have a look at pulse-jack-post-start.sh and adapt the bottom to your own keyboard. There is not much to do and it should consist only in changing your keyboard identifier and the naming.