Just for clarification Tyranids never get extra attacks for additional weapons as it states in the codex that this is already reflected in their profile.Having two close combat weapons gives a bonus attack, like assaulting gives +1 A. To my knowledge (which is limited to two codexes) this is never reflected in the profile. So base 2 attacks plus two CCW gives you 3 attacks.
As much as id like to say that a warrior with 3? attacks plus a pair of scything talons and a pair of rending talons gets 6 attacks I dont think my opponent would be very happy