I've read through all the mods on the first page and decided to give it a go.
I started by adding lead strips to the driver surround for mass damping.
I took off the internal felt covering the bass ports and placed that one the back of the driver.
I put masking tape over the ports on the outside to fine tune the bass. The cups are sealed with masking tape instead of the screws during the incremental modding process.
I took out the 3.5mm unbalanced socket carefully with some pliers, preserving the upright and semicircular stanchions holding the socket in place. I filed the semicircular portions down a bit to fit a 4 pole 3.5mm socket.
I hot glued the socket in place.
I added bitumen paper to the wells either side then covered with loose cotton wool roll.
The socket from the outside:
3.5mm-4.4mm balanced cable:
I'll put the pads back in the groove and fine tune the bass ports after that, putting electrical tape on the inside once I decide how much bass I want.
Balancing definitely improves the separation and adds a little sweetness, joining up the registers more coherently.
I've got some more angled pads coming to complete this mod. I also added a Sennheiser HD600 4-blob headband under the Fostex one for more comfort.
Once I get the tuning right I'll probably sell this on and the DT770 I've modded.