Intellijel Mixup has a mute switch per channel. It is 3 stereo channels and each channel knob completely attenuates the signal ccw.
Edit: actually, a little bit more complex than I thought.
“Inputs 1 and 2 are single-channel mono inputs, each with its own mute switch and level control; Input 3 is a dual-channel stereo input with a shared mute and level control; and input 4 is an auxiliary unity-gain, non-mutable stereo input.”