I think DK means 'double knit'.
Seems a bit tedious to go through and split the plies of all that yardage. I guess if you're a spinner it may work; but that's an aweful lot of work to do on a total gamble.
It's only a pair of socks and they don't require a whole lot of yarn, so I'd just buy more yarn. (Also consider your dye lot too. If you have to buy a new dye lot, alternate lots within the sock, so that difference can be hidden - that way, you won't end up with two different color socks.