Tim
You neglected to offer any information on what failed in your model over the weekend. I am guessing power failure of some sort or something that caused the second system to go to sleep, maybe even a loose crystal.
In other failure circumstances things may not be so easily manipulated. Imagine a surface hard over, wide open throttle, intermittent response good and bad from one system. All of these additional scenarios are prevalent and can and will happen. Believe me its no easy stable flight thing when you have a control surface hard over and are fighting with mushy inadequate response from the opposite side of the model. Been here done this!
Just a thought; dual RX's offer very little redundancy unless you have an RX failure! Batteries fail occasionally (with todays products its actually pretty rare), switches fail and wiring connections fail weather its brain fade, inadequate rigging or? This is true with one two RX's. Dual batteries and switching systems are simple old news and quite adequate, IMO. There is something to be gained when more than 8-9 servos are used, as other stipulated. Modern day high end RX's have been burned down to failure and are capable of withstanding 20amps intermittently without issue, in fact sustained spikes above 30amps were introduced before failures occurred.
An effective alternative for two RX's is the use of Matchboxes or Smartflys Equalizers when servo count is high on specific channels and these devices offer the ability to use separate batteries, again.
I'm a firm believer in utilizing choke servos. These are no more likely to fail than any other servo on board, in fact I'd guess they last substantially longer as they are exercised much less than any other servo on board. Another safety feature with little to no reason to think they'll fail, IMO. I like to use mine to start the engine too, you can fire the engine, choke-on and flip the switch all in one starting effort. Or you can use some other type of electronic or mechanical KILL switch system.
Modelbau's Power Box is has been refitted with a regulator able to handle the higher static voltage of the Lithium-Ion technology and a new switch assembly (Emotec is releasing there refitted unit in September, same reasoning), probably no secret bells or whistles. One can use the standard Powerbox NOW with the regulators in line, before the Powerbox same as your using them now (several TOC pilots used these as described above).
Something I am not clear on and in fact completely disagree with is Model Baus reference to "when one battery diminishes to the pre-set level the second one will immediately cut in and provide the necessary power-supply to the RX and servos. Utilizing Lithium-Ions in this scenario is not recommended... Both batteries must be on line with the high current demands that fourteen digitals servos can will require. This is the crux of the Lithium-Ion technology to date. What happens is under load without adequate capacity the voltage drops well below the desired output. This the very reason these cells are series-paralelled wired. Two things are realized with this methodology, additional ampacity and power supply redundancy within a single battery pack (generally the larger packs are comprised of two pair of two cells in series-parallel configurations). Hopefully this information is relevant to the earlier models for NiCd/NiMH applications or a typo/translation issue. In any event I don't agree with the concept.
The only redundant feature offered with the Power Box system is battery ganging to the power buss. Both Emotec and Model Bau offer single switch failsafe ON system features. Redundant power sources are available in several different methods for our systems without benefit of these gadgets. Some like the KISS concept. One could argue that all this additional gadgetry introduces several additional failure modes! And they would be correct, IMO. I am using the Emotec gadgets in my new models together with Lithium-Ions, plug "n" play wing and stab servo connections, custom built wiring harnesses and the works. Hopefully an ounce of prevention will amass pounds of good luck!
http://www.modellbau-deutsch.com/e/h.../power_box.htm
http://www.emcotec.de/download/download.html