I'm designing (probably over-designing, but I want the experience) a four-input, four-output, stereo mixing setup for my PC setup, but I'm concerned that just tying all the ground lines from that many inputs is going to cause ground loops and similar issues.
The inputs are going to come from my PC, an FM radio board, and other headphone-jack style input sources, while the outputs are going to go to my PC speakers, a pair of headphones, the line-in jack on the PC, and a spare auxiliary output.
Would capacitors between the inputs and the amplifiers be enough to decouple things, should I use op-amps in differential mode (like this example shows, though adapted for stereo), or is there another option?
Granted, in a couple of cases, like the PC's input, I'll have to tie the ground to actual ground, as I'm also passing the microphone signal through from the headphones, so I can't cause similar problems the other way around. (I should also be able to get away with using the same ground as the radio module, given that I'm actually providing it with a ground reference, and the fact that it's using the same ground for the headphone jack as the one it's given)
I should note that I'm still in the process of designing the whole project, which means that I don't have a power supply chosen, haven't selected volume controls, and don't know what values to use for any of the resistors yet. (yes, I'm asking this question very early in the design process)