Multiple Attacks is for physical combat though, isn't it? Matrix actions are detailed in the Matrix section.
I may be reading too much into the sentence: "Note that specialized Matrix actions are described on page 179", but Multiple Attacks does state that it must be used with the Attack Major Action, which then refers to the Combat section.
If you are attacking something in the Matrix, you would use the Data Spike or Tarpit Matrix Major Actions, not Attack. This seems to be backed up by the fact that there is a separate Full Matrix Defense action, so you wouldn't use Full Defense to defend against matrix attacks. At least, that was my understanding of the Matrix action rules.
Also keep in mind the limits on Major and Minor actions. You already accounted for this...