The Dolphin is rigged with RAF wires, which are flat steel bars with threads at the end.The crosses besides the cockpit are not two crossing bars, but 4 bars pinned with connection plates in the middle. This can be loosend by a screw/butterfly nut connection to act as emergency exit when the plane is lying on its back. Otherwise it will be hard to get out for the pilot due to the special wing construction. In front of him are the Vickers MGs and on the back the header tank.I mean the part on top of the "t" in this picture:Source: wingnutwings.comCheers,Frank
Crossed rigging was tied together to reduce vibration, as you mentioned, to reduce wear of the rigging at the intersection, and to stiffen the whole structure.