No problems at all remapping them. The standard car is over 500Nm so I am slightly suspicious that the maximum torque of the gearbox is only 600Nm. However they don't handle torque anywhere near as well as the Tiptronic. One of the Members on here is running 900Nm on his 3.0 TDI tiptronic.
I believe that 650Nm is achieveable on the S-Tronic as JD engineering seem to do a lot of 3.0 TDI running that.
In the interests of longevity though maybe 600-620Nm might be a little better. Depends on how risk averse you are. As you can see the standard car makes 520Nm so Audi would not cut it so close on the torque handling capability of the gearbox.
A good tuner will be able to deliver what you want and even with a 600Nm limit you can get over 300bhp .
If you are anywhere near Manchester Rick at Unicorn Motor Developments is in Stockport, He has mapped many 3.0 TDI cars for members off here including my own.
Lat time I was at Ricks we had mine running with just over 600lb/ft which is 810Nm and it wasn't slipping on the dyno but It's a daily and it's the original 100K mile clutch so it was tweaked back to 550Lb/ft 750Nm . I have seen maps for a 3.0 TDI manual running over 850Nm but I believe that had a non standard uprated clutch. I haven't seen any available but there are specialists who could uprate them I am sure for the right price.
Thanks Bobby that is reassuring. The car is daily driven and needed for reliability, I've been searching for any issues after a remap and cant find anything so far so looks like a remap is on the cards soon