Winn, when I bought my floors - I bought them in Brooks, they recommended a fitter as well, whom I rang and who was nothing but rude and unhelpful and when I explained the price I was quoted through Brooks for his services he said there was no chance with the kind of stuff I thought needed done to it. I think if I had booked him through Brooks it would have been 600 Euros, but that was assuming the floor was in perfect condition - they never tell you that bit when you buy the flooring. So the guy I went with came recommended by Woodworkers in Terenure. I'd say there is very little chance that you will get any help or refund from DK, I think you have only two options - cut your losses and get someone else or try and find someone who will do the "ground-work". If you want I can give you the details of the guy who did the job for me, he might be willing just to do the levelling job. He also put some sort of sealant underneath the dampproof plastic layer as he measured the moisture in the floor and it was slightly too moist for wooden flooring. I ordered the plastic layer and chipboard from Brooks, which they deliver, and then he did the rest for me and it took him a week for everything. I was a happy customer.
I put lots of self-levelling compound onto my kitchen floor - it is not as easy as it is made out to be, and it does take some time to dry out properly. You'd have a good bit of delay if you went down that route... Good luck!