Spurs don't need a defensive big, anyways..
Duncan, while struggling on offense, is still at least a "good" defender, and Splitter is a solid all-around defender..if the Spurs acquire another big, he needs to be competent on offense, tbh..if not able to create for himself, then at least have the capability of making a jump shot..
Asik is a great defensive player and easily a superior interior defender to Splitter, but his offense is worse than Tiago's in every facet..acquiring a better interior defender but a far worse offensive player makes absolutely no sense for this Spurs team, tbh

..Asik is essentially a zero on offense, opposing teams don't have to respect any facet of his offensive game..at least Splitter is a terrific passer and a very good pick&roll finisher..
The Spurs were an elite defensive team last year and they have looked the same so far this year..if they make a move, I'd say they need a backup guard that can create(Jameer Nelson, for instance) or a small-ball 4/athletic PF(although Kawhi + Diaw 2.0 is probably sufficient)..