As requested (if a little bit slow…), here's the key details
Price (gulp!…) £2490+VAT - i.e £2988 gross. Sadly, they don't give A8 forum members a discount (we've tried...
)
For that, they completely recondition the gearbox, replace any parts which are faulty/not performing to spec, including fitting an upgraded torque converter.
The warranty is 36 months or 100,000 miles, whichever comes first, and that was what swung it for me, ultimately, along with their reputation.
There's also a chargeable Warranty service at 12 months/12000 miles, which costs £155 (as quoted by David s8).
I've been very happy with the performance since this was done, though I've only done about 8k miles since it was refurbished just over a year ago, and would recommend them, if you can bear the cost of it. Hope this helps.