Microcontroller GPIO in audio circuits
I would be worried most about capacitive coupling. While most of the digital noise is high frequency, it oftentimes has some low-frequency components, so a high-pass filter does not eliminate everything you would like to have eliminated.

You might want to put guard traces around the digital control signals, and make sure your switches have proper decoupling between the control signal and the analog stuff.

For the MOSFETs, dont forget the gate-to-drain capacitance (also known as Miller capacitance because it is the source of the Miller effect that increases the effective gate capacitance). High-frequency noise present at the gate couples to the drain. While your MOSFET is on, it is not a problem, because you have a low-impedance path between drain and source, and source it at a low-impedance (virtual) ground. The virtual ground (which should be properly decoupled) will absorb the coupled noise. On the other hand, while the MOSFET is off (i.e. gate at ground), any noise at the gate is still coupled to the drain, but now works agains the impedance of the resistor feeding the signal to the mute switch. The higher the resistor is, the more coupling of noise into the signal will be observable. This is especially an issue if your design works with separate ground planes for the analog and digital part. If the digital ground and analog ground is tighly coupled, the noise level while outputting low is most likely no issue.