This is a box designed to house the DIY RE "HC1 High Current Headphone Amp" a brilliant little ($10) headphone amp from the folks at DIY Recording Equipment. I've also designed it to be a two in, one out switch so you can feed two audio sources on TRS jacks into the back and switch between them. I also added a XLR pass through just for kicks. 

Here's some links to the parts I used, however you can swap these out for whatever you want if you don't mind resizing some holes. 

DIY RE Headphone Amp Kit - https://www.diyrecordingequipment.com/collections/studio-essentials/products/hc1

Any two position switch, I used one like this - https://www.altronics.com.au/p/s3032-6-pole-2-position-wafer-rotary-switch/

With a chicken head style knob like this - https://stompboxparts.com/knobs/chicken-head-knobs/

3 pin XLR chasis mount female - https://www.swamp.net.au/neutrik-nc3fd-lx-female-xlr-panel-mount-connector

3 Pin XLR Chasis mount Male - https://www.swamp.net.au/neutrik-nc3md-lx-female-xlr-panel-mount-connector

I sized everything for M3 heat set inserts - https://core-electronics.com.au/brass-heat-set-inserts-for-plastic-m3-x-4mm-50-pack.html

Any questions hit me up - Good luck!