digitally controlling is different from digitally processing. you can keep the signals analogue and implement the control digitally.
build a diagram to show your requirement it will easily illustrate your idea than explaining. Based on that you have to develop your design.
if you want it remote you need remote decoder
get different functions from the decoder out and define the control inputs for your design
select ICs for volume control, muting (switching), selection and mixing...
i feel you have a lot to work out with data sheets and find out suitable ICs.