SB710-equipped motherboards can unlock cores, not just SB750 ones, as both southbridges support ACC.
The problem with unlocking Kuma CPUs is AMD itself found they'd unlock very early in their production, so they stepped-up their disabling/lazer cutting of the additional cores. Early samples would unlock, with some of them becoming fully-functional quads, but later ones wouldn't even unlock. I have a 7850 that speaks to the latter. It simply won't unlock, despite trying it in 3 different motherboards.