Im goin with prime... just cause there are multiple of them doesnt mean their power stacks, its just repeated (6 billion times repeated) attacks that wont do much to him at all....
If I punched a boxer it wouldn't hurt him, but if I did enough it would because his body would weaken. Same thing with Prime even if it doesn't effect him at first it will eventually.
But yes a normal Daxamite should hurt him at least a bit.
If this is countdown Superman-prime... why would he have to fight them? He could just pick and choose which ones he wanted to fight. And when had enough... he could just bust the planet...
But if this is six billion superman level beings, fully charged... then I think its safe to say that he could come out of this hurt, but with about 6/10...imo.