The problem using such a solution is that I wouldn't be able to use a button box based on an Arduino Uno or Mega in conjunction with my Thrustmaster hardware on the PS3.
This because I already need one Arduino to act as a controller for use with my hydraulic handbrake, and I plan to make a center console using an Arduino Uno (or mega) for those buttons.
That's two controllers, plus the fact that the Arduino Mega could act as a double controller (emulating two DS3 controllers).
Now I've looked at the hardware in the GT rim just now and it's quite simple actually. There is no microcontroller in them, just two static shift register chips. Namely...
StMicroElectronics HFC4021B (SOP):
http://www.st.com/web/catalog/sense_power/FM140/SC1798/PF63016?s_searchtype=partnumber
That together with the Panasonic 104 surface mount resistors:
http://www.digikey.com/product-detail/en/ERJ-8GEYJ104V/P100KECT-ND/203250
And a single 104 surface mount capacitor per chip:
http://uk.farnell.com/avx/08055f104kat2a/capacitor-0805-100nf-50v-x8r/dp/1301790
The hard thing to get I think would actually be the 6-pin Mini DIN male chassis/panel mount connector that Thrustmaster uses in their steering wheel bosses to make the connection.
I will dig a bit deeper to see if I could use the internal electronics.
Thanks for the offer though, John.
ps. I have made a image set on my Flickr account with images of the electronics. Thought I made share for all of you.
GT Rim Electronics:
http://flic.kr/s/aHsjEnC7zz