Actually there is no (positive) value of AP that makes BB>HS for even 3 targets let alone two (assuming a weapon of at least 463).
heres the graph for 3 if you don't believe me (graph is for 463 weapon)
That said, you're still right in that more adds there are, the more damage you lose by death striking. The numbers I gave you were based on 3 targets, though regardless of how many you have it's still always your first priority to stay alive and maintain stability, so you should never feel guilty about death striking no matter how much dps you lose.