But the majority of places you go, its not possible to do a LR Sub setup, when you use the desk for touring, and not as part of a complete production. But yes, it works quite well in places with seperate subs and ultra sub for instance.
I think it would be great to just have an extra box that you could switch between 6, 12, 18, 24, and 48db/oct. Problem solved. It certainly cant be a DSP problem 
I like the digico desks, but they have a learning curve thats a little more challenging than the rest I think, but are excellent for a tour production!
