the DD-6 warp mode gives a very convenient foot pedal self oscillation effect, that, is super easy to engage compared to bending and twisting knobs on the DD-2 while you avoid damping your strings or deadening your sustain while bending and twisting.
The DD-2 and DD-6 are functionally quite different due to the many enhanced features in the DD-6, albeit a somewhat sterile sound; one pedal of the two has mojo, the other doesn't, imho.