After pulling out every hair I have on my head trying to figure this $4.7m shiny bucket of bolts out, I am finally able to drive the R10 TDI like I mean it. Out of the dealer, I had the same problems as you guys here and I tried everything suggested with no luck. Bear in mind I am a motorsports purist at heart and do not believe in traction control while racing, even if my competition does. TC & active steering, ASM all set at 0 or off.
The key (for me) is the Limited Slip Diff. I turned the accelleration down to 6 and could then gas it out of the corners. Finally I can drive with the confidence of Emanuelle Piro and Alan McNish (minus the skill level, of course!) Once the massive on power oversteer was settled, I could get a feel for the handling characteristics of the car and start tuning it for my specific driving style. First, the ride height seemed weird so I evened the front and rear with maybe a little rake putting the rear 2mm higher than the front. The car actually has a lot of understeer and I like it best with a softer - than - stock front springs, bar and dampers in both compression & rebound. I also went 1 step stiffer on sway bar in the rear. After that, it's just a matter of tuning the gear for the track. For more confidence, the downforce can be cranked all the way up for shorter tracks without hurting the top end speed.
I'm still not convinced it would have been better to be more patient and waited for a R8 or Pescarollo Judd to pop up in the used dealer.
I hope this helps and keeps other rivers from going crazy and wasting hours in practice mode without earning money! Cheers and good luck!