@deckingman @Exerqtor @jens55 @OwenD I got it roughly configured and working----3 stepper motors on the bench and if I select T0, D0+D1 spins, if I select T1, D0+D2 spins. Thanks again for your help 
the next part is to add icing on the cake, and this will be a filament Y splitter, with microswitch on all 3 paths + a bit of (maybe a lot of) conditional G code to make this idiot proof 
I have attached my config.g here, hopefully this can serve as a starting point for someone