Why not use both the IBEC and the 2 switches/batteries? The second switch and battery are there in case of a switch failure, as well as provide the ability of supplying a LOT of extra power to the receiver and servos.It's almost a necessity in the case of larger digital (read that POWER HUNGRY!) servos.
In the case of A123 batteries, the second battery on that setup is optional IMHO. A properly sized single A123 is capable of supplying plenty of amperage for that setup, and power to the second switch can be supplied by a second power lead coming from a single battery.