So here is the build post:
4 screws (#0-4 or 1.2mm Phillips) are hidden behind this foam. This will remove the driver housing.
The drivers are sealed in with glue. It's mostly easy to break the seal and remove the back of the housing.
Be careful here, as the 32AWG stock wire is very fragile. You will have to remove the glue holding the wire in place as well.
The almost finished new cable. 22gauge Teflon insulated.
My first attempt did not work. This hits the back of the housing.
I ended up running the wire through the stock location, after enlarging the hole.
I glued the new wire just like stock.
New hole on the right side. The HD428's have a single wire coming out the left side only. I wanted separate wires. This is to allow me to convert over to balanced in the future if I wish.
The re-assembled headset.
I used a Y-split for now, as I do not have a balanced amp. I also don't have any cotton wrap or techflex... That will come in the future.
After all this mess, what I hear is NOT a fantastic amazing change, but I do hear more presence in the high bass/low mid frequency.
That MAY be do to being able to hear much higher frequencies more better, and not a boost to low mid at all. I can hear the sharpness (or transience) of brass and reed woodwind instruments.