I built a custom output module with an output buffer, headphone amplifier, and a 440Hz square wave reference oscillator. I made the panel using 1.5mm anodized aluminum with the print graphics feature from FrontPanelExpress.
Each rocker switch mutes its specific output. The output and phone jacks are 1/4" and the phones are driven in stereo from the mono input signal.
The rocker switches are mounted on 0.25" standoffs so they are nearly flush with the panel.
The PCB is hand wired and uses my A440 IC and my Headphone design. The trimmer closest to the front sets the gain of the output jack from unity to 10X. The trimmer closest to the rear sets the gain of the headphone amplifier.