As MJ says, the controller is in the boot, above the battery. I have a photo of it somewhere, but can't find it. It is posted on here on the forum, but it's a black plastic box maybe 10x5 inches in size and about an inch thick, with some heavy cables coming from it. There are also a few fuses just above it, though not sure if they are relevant.
As to the screen itself, I believe there are four connections to it. One in each bottom corner (can't find that photo either), which you can maybe see in the gap between the dashboard and the A-pillar. The top two you can see if you remove the lighting module up by the mirror.
EDIT: Found the picture of the module in the boot:
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts
My DIY jobs -
Replaced alarm horn,
Replaced Coolant Temp sensor,
Updated RNS-D firmware,
Installed Reversing Camera and Digital TV,
Dashcam Installation,
Retrofitted Rear Blinds,
Auto-Dimming Rear View Mirror,
Chrome Boot Struts
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2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights
My DIY jobs -
Fan Jet Windscreen Washers,
Retrofitted Electric Side Blinds