Nero used to have a feature, that would allow you to burn to multiple (identical) drives at once. Does Nero 6 not support that anymore? IIRC, retail-purchased Nero 5 supported two drives at once, and you could purchase a special plug-in that allowed supporting more drives, up to a total of 32 drives as once.
I used to burn multiple discs in (different) burners, using multiple instances of CDRWin.