I wrote to autotech about this very question and here's their response:
ESP would continue to work just fine with the Quaife differential, as it
acts independently of the internal workings of the Quaife. The differential
installation itself is fairly intensive labor. Tearing the gearbox apart,
installing and possibly shimming the differential for correct clearances are
fairly specialized actions, and may be better off left to a professional VW
technician with access to all the proper tools and references. Hope that
information helps a bit!
Autotech Sales Staff
Damn I wish there were more people like me on this forum.