I had a similar problem with my 99 Grand Jeep Cherokee...
The remote buttons on my steering wheel would control the stock radio/cd changer.
(Mine had an 8 pin connector.)

I spent about 10 hours trying to figure out what I could do, to comply with the Empeg...
So I could still have that luxury/convenience.

My advise to you is this:
The easiest way to make this work is to use this "adaptor harness". It's almost like the one you described, except it will produce/send a frequency.
(Taken from this FAQ entry.)

This would avoid all that wiring/trouble.