I replaced mine several years ago, following these instructions on the audipages site:
http://www.audipages.com/Tech_Articl...chreplace.html
It's very detailed and they specifically mention which bits are a PITA to do, or just awkward to reach. The only comment would be on point 6, where he says to use a small jack to support the transmission. If possible, either use a scissor jack or bottle jack, as they give a proper straight up lift, whereas a trolley jack (my only option at the time), isn't straight up. From memory, most of my time was spent on the top transmission mount bolt, (point 8) either getting it out or putting it back in again. Looking at the photo on the RS246 thread of the 'mod', I don't think you could do anything to make it any easier on the A8/S8.
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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