it dependsheavily on the tyres fitted. with the crossclimates, no steering corrections are EVER necessary, while the Hankook ventus prime2 are more like jack russels running to anything catching their attention.
The weirdest and most addictive torque feeling , which you don't get with eQ2 is that of the mechanical Q2 I had on my 147. You'd want to go round the roundabout again but you don't notice what the abs is up to on the Giulietta. The fact that it's faster and easier isn't the point!
Yes, I would like a quaife or Q2 in my TCT, combined with the eQ2 you'd get some sort of locking diferential. I can sometimes feel the eQ2 engaging, whe going around a fast corner, thinking I'm near the edge of grip, putting more power down and feel the line tightening instead of widening.
Yes, it can be combined. I can't tell you which system would be dominant (I somehow expect it might be the eQ2) but once one system reaches the limit of it's transfer capabilities the other will step in and add to that. Both react to speed differences between the left and right axle, and both add friction to the speeding side to slow it down. Difference is that the ATB needs resistance on both sides (a lifted wheel means no torque transer) and the eQ2 doesn't strictly need that. Depends on the programming.
Since both do the same, they might reinforce each other, but they won't fight each other. However, torque steer is increased and if you don't realise that or expect the opposite you'd describe it as both systems fighting each other.
Anyway, Autolusso offers a Quaife for the C635 box. Someone will have it installed.