I forgot to say in the 5.1 set you see the green[lime] black and orange are used to push that set [#4 page 2 of manual I linked ] but a simple 2.1 like the z3 just uses the green[lime] from the pc onboard [#4 page 2 as well from its manual]
so at least with them your onboard audio is equipped and good for there use ''There are 4 analog outputs (grey - side speaker, black - rear speaker, orange - central/bass, lime - front speaker).
2.1 always been good for me I got enough clutter around my desk and 5.1 set up just adds more to that I don't need to deal with [opinion] lol....