Those breakers sound amazing! Well worth poking around all those sport car parts just for the fun of it.
There are quite a few potentials on ebay, lots of A6 C5 Tdi's being broken.
http://www.ebay.co.uk/itm/BREAKING-A...wAAOSwstxVFdJD
http://www.ebay.co.uk/itm/03-AUDI-C5...wAAOSwNRdX4Y0g
And 01E but with the 4.375 final drive
http://www.ebay.co.uk/itm/AUDI-A6-C5...UAAOSw65FXrxg-
I would be curious to see how the 3.75 first feels in a S8, the standard 1st is 3.5 so not far off. I do agree though that the 3.5 stock 1st gear is mental anyway. But fun on some occasions