If you install open-roms (for sid replay) you might want to
edit your ~/.config/ocp/ocp.ini with
  kernal=/usr/share/open-roms/C64/kernal
  basic=/usr/share/open-roms/C64/basic
  chargen=/usr/share/open-roms/C64/chargen

For better MIDI playback you might need to install the
EAW patches (Eric. A. Welsh), find an installer at
(mind you the licensing of them are not clear)
https://github.com/alexmyczko/autoexec.bat/blob/master/config.sys/install-eawpats