I just did it a couple weeks ago for the first and last time. I modded a version 7 PS2 (there is about 12 of them and the installation is different for each one of them) with a DMS 4 lite. I did a lot of research and reading on the web. Do not expect any kind of instructions with the chip. Mine came in a brown enveloppe with nothing else in it. At first, I though the enveloppe was empty.
Anyway, I grabbed the bull by the horn and opened the case. Well, well!!! When I saw what I was dealing, my first reaction was to close it back right away but I promised my son to do it so there I went. I would compare the soldering process to open heart surgery on a house fly using a butcher knife. It took me four hours to solder 17 wires the size of a noze hair.
I closed the case back and plugged it in, flash the Bios and waited. Guess what! The dam*** thing is still working. And not only it is still working but it plays back up games. I was as a happy as pigs in sh**t. Not that it plays back up, but that I did not screw it up, period. I still don't know how I did it.
Next time I promise something to sonny, it will be a pre-modded console!!!!!
Morale of the story: it is feasible, however make sure to go to church and burn a few candles before plugging in your soldering gun.
Have a nice day