I'm guessing the finger condom has something to do with brake lines... if I were a guessing man... haha
I did all the pinout sheets for the DSP system when I first got my RR (Was it REALLY 5 years ago?!?) because I had bits of the system missing, or not working - and it was more actually to aid me in fitting an aftermarket head unit...
Believe it or not... I have never ACUTALLY heard a P38 DSP system working.... my one was missing the DSP amp, and my '00 Vogue had the DSP amp, but it's toast, and hence has got one of my DSP replacement amp boards... (which the wiring charts were helpful for aswell!)
The way I see it... if it's meant to be able to work as an CD Changer input, then I don't see why it shouldn't work plugged directly into the head unit, vs at the other end of a long bit of cable!
I had a look on the Grom website with the DSP adapter you linked to, and I can't even think about where you would hook it up to on a P38... as Sloth says, maybe more geared towards L322/(Maybe X5?) and saloon models - maybe they changed the audio systems so the DSP amp handled ALL the inputs and switching.. The P38 DSP does Nav, and phone (if fitted) but luckily for us, the front end of it is still fairly standard..
I wonder if some of the changes on the 322 were because they went to an all-in-one unit for radio/navigation in the dash, rather than separate like we have?
'06 4.2 Supercharged Black/Cream "Jess" -- Bought April 2021 (NZ)
'01 4.6 Vogue Black/Lightstone "Snog" -- Bought Jan 2012
'99 4.6 HSE Cobar Blue/Lightstone -- Sold March 2009
'95 4.6 HSE Epsom Green/Tan -- Traded June 2008