There are other ways of connecting an external device to the Disco 2 ICE system without the need to replace the head unit.
There is a company who can install a 3.5mm stereo socket for a fee, about £75 I think.
The way which I did mine was to fit a small FM modulator actually in the aerial lead, not the type that radiate or transmit the signal to the radio. I can say that it seems to be a reasonable method without the problems of interference.
There are some other methods that involve injecting the signal from your device into the wiring from the CD player (the driver's seat).
There are downsides to changing the head unit, the first one is the steering wheel controls won't work without the proper adapter in the wiring and the output from the replacement radio is likely to be too much for the input to the power amplifier (under the passenger's seat).