at least in part anyway.
You are quite correct in stating that any fault that develops within six months of purchase is deemed to have existed at the point of purchase unless the supplier can demonstrate otherwise, but.........
Under current consumer law you aren't automatically entitled to a refund, and certainly not to a replacement. The supplier has the right to attempt a repair and return the item to you "within a reasonable time". What is "reasonable" in terms of time isn't defined in the regulations - each case is judged on its circumstances, should the matter end up in court.
In many cases it is indeed faster to deal directly with the manufacturer - particularly in the case of complex electronic items which could not be repaired by a retailer in any event. To protect your position it would be worth writing to Dabs to record the fact that a) the drive has failed, and b) that you are dealing with the manufacturer because you feel it's the shortest line between A and B.
Make sure that you include a line in your letter to the effect that although you are dealing direct with the maker you consider Dabs to liable for the repair (or replacement, should a repair not be feasible) and that you reserve all your rights in law.