It is much easier to insert and remove the muff body clips by rotating them 90°. The plastic stud underneath is oval in shape and is indicated in green on the image.

Remove the pad by inserting a large flathead screwdriver or butter knife just underneath the plastic backing plate of the padding and continuing all the way through to the muff shell. Then twist forcefully, and the underlying plastic should pop off. Using a finger is nearly impossible on the first attempt, but works on subsequent attempts.

Now it's free! But be careful to not twist or yank the cable.

Take a T7 bit (thanks Laz) and start opening it up.

The backside view of the earcup shows the circuit board. There is a cavity on the ear cup, but it looks to only be as deep as necessary. Wires going to the speaker are strain relieved with glue (not pictured)

Another view shows the BES2000 SoC

The ordering of the colors of the wire: Blue-Gold, Green, Red-White, Blue, Orange, Red. Thanks Grant!

Contains a battery and connector PCB. Battery type is 603040 lithium ion, dimensions are 6mm thick X 30mm tall X 42mm wide, with a 3-pin JST (includes thermistor apparently)

The left side speaker and its cavity are 37mm wide and 16mm deep. There is extra space underneath the speaker, maybe for better acoustics. The rubber gasket is glued on. The right side had a similar cavity, although not as deep.

Proper earpad replacement cups are GEL-HYG (specific to WorkTunes). Peltor-style replacements don't work for some reason.