its not need.. The only time the quaife has issues is when it loses full traction to the inside wheel since it multiplies the tq to the outside wheel. 0 times any number is still 0 and thus will behave like an open diff, minus any preload. The elsd will kick in at that time however and any braking tq applied to the inside wheel will be multiplied to the outside. Essentially u make the elsd much more efficient instead of an open diff only transfering an equal force to the outside wheel.
My thoughts are that the elsd compliments the quaife really well...