Can multiple AD9508 be synchronized with SYNC Pin?
I suppose you have the same clock going into two or more AD9508s. If this is true, maybe we can find a buffer with 8 outputs or more for you. Just tell me what output driver you intend to use.
But if you really want to use multiple AD9508s and you plug the same clock into all of them, then powering or resetting all AD9508s with the SYNC pin low and then pulling SYNC high simultaneously on all AD9508s should align all outputs from all AD9508s.