Glenn,
I have the same problems with growing from seed. We don't get enough sunlight here for the plants to behave as in habitat.
Rose, you did the right thing in bringing them in. Don't worry about the dormancy issue, but also do not give up hope if the seedlings do die back. I have had them return against all expectation, so they can in fact form small tubers. For me, the process contines for a couple of seasons and then the plants wane and die.
Plants from established tubers fare much better, but there are few sources for material not field collected. Phill Mann in Australia continues with his efforts to introduce these species to In Vitro culture. He says the introduction is successful, but that the plants are difficult to adjust to the reversed seasons.....a fact I can attest to. I am delighted to see the return of one tuber of D. finbriata. I started with 10 tubers, but only this one has adjusted to our reversed seasons.