I bought 3 SFF-8643 to SFF-8639 cables from different vendors and none of them worked with the card. The same cables worked with a cheap M.2 to SFF-8643 adapter. I ended up buying Dell cables and backplane for the GY1TD.GY1TD uses PEX8734 (32-Lane, 8-Port PCI Express Gen 3 (8 GT/s) Switch).
The pinout is not compatible with cheap SFF-8643 to SFF-8639 cables used with M.2 adapters. So you will have to use the whole Dell kit again. Which increases the cost even further. Which makes it not that interesting to me at the moment. Unless someone can figure the switch config to remap the lanes to make it compatible with the cheap cables.