He11ix means in which of Sollux's quadrants Aradia and Sollux are, Stormspirit.
I don't remember it being really said in canon, and I'm really not sure either.
There's plenty of evidence for either, but Feferi once used a "" for Sollux and referred to Aradia as Sollux's close friend.
And Aradia didn't seem to have much trouble flip-flopping between love and hate for Equius.
I guess the most likely would be Sollux Aradia and Sollux Feferi then.
Unless Sollux has 2 moirails/matesprits. Which would also make (some) sense since Sollux and Feferi had been feelings jamming.