Aagaard recommends 9.c3!, "the key idea is to keep c4 vacant for the queen". 9...Nf5 (9...f5? 10.Qa4 Kf7 11.Qb4!; 9...Ng6? 10.Qa4 Bd7 11.Qc4!) 10.a4 Be7 11.Bd3 0-0 12.0-0 Nh4 13.f4!.  All of the previous exclams are his.  Strangely enough he now has a subnote that goes, 13...exf4 14.Bxf4 Ng6 15.Bg3 Ne5 16.a5 a6 17.Nd4 Bf6 18.Be2 g6 19.h3 Bg7, "with very little if any advantage for White, Matulovic-Moutousis, 1990".  So perhaps 9.c4 is better, however his book doesn't have any continuation that leads to a White advantage.