I know that this question is about XX9s specifically, but realistically this same question will trigger for any combination of a critical dealing a face up damage card and the Standard Critical Effect.
Again, this question goes past FAQs and needs an errata to one or more game rules or cards. This Errata needs to specifically address how critical effects that deal damage cards are counted during the resolve damage step of the phase and whether they count as the first damage cards dealt by the attack.