I don't think that D. dichotoma "Giant" requires a dormancy. I've had one for three or four years and it's never stopped growing - it's become a real monster, too. A few pots of cuttings that I didn't have room for inside last Winter went dormant and came back, but I certainly don't think it's necessary. Where did you hear that, NaN? I'm a little surprised to hear you treat them so delicately. I've heard newer growers talk about dormancy for binata strains, but the formal concensus had always seemed to me to be that they didn't have a dormancy and behave like tropicals other than being able to come back from the roots after a frost.
I'm curious now - maybe I'll leave some of my dichotoma and "extrema" plants outside this Winter and see how they do. Last year the pots of cuttings maintained their foliage through several days of frost, then snow and hail, before I moved them into my friend's garage where it hovered just above freezing. They didn't drop their leaves until he kept them unlit for like three or four weeks, but when he got the lights set up they all came back. Out of five pots of D. dichotoma and about thirty more of capensis, they're all as good as new this year.
~Joe
PS - To answer the original questions - treat them all the same. Basic mix of peat and an inorganic filler like perlite, ceramic chips or sand. Keep them indoors and they'll do fine; keep them outdoors and they may die back to the roots after a frost, after which they should probably come in until the risk of frost has passed. But if it doesn't freeze often and you put them in a well-protected container (like an in-ground bog) they may well just take to life outside permanently. I'd recommend keeping them in separate pots, as one will eventually choke the others out in all likelihood.