A lot of misinformation there.
There's no "manual transmission mode" in the factory RS6 ECU.
Basically, untuned you can drive it both with TCU and without TCU.
With TCU connected your ABS/ESP will still function, but the drive itself might be a bit more erratic (anti-jerk algos running in the ECU still accept signals from TCU, which goes bananas without the actual transmission).

Reverse wiring: https://www.audizine.com/forum/showt...a-5-speed-swap

Stock ABS unit can be retained and made to function with MT with proper ECU programming.

Actual clutch switch "advantage" is that (when properly programmed) ECU actually *knows* you have disengaged the clutch and acts accordingly. It's *strongly" recommended to wire that in. People actually report "night and day" difference with it: http://www.rs6.com/showthread.php/33620-Nubcake-6-speed-tune-review