I've been charging 10s packs (2x5s in series) on both 10S and 10XP chargers since these chargers hit the market. I have always connected the balance connectors as shown in the photo by Zeeb. I don't use the boards but use adapter cables to go from one 5s ( the low end) to Ch 1 and another from the other 5s (the high end) to channel 2. It is logical and it works. As far as I am concerned this is the official way to charge 10s packs.
Jim O
Jim,
Same as you, although I still keep some of this adaptor boards around and use them a), when the adaptor cables are broken (happened during a contest), and b), when charging some old TP packs that use non-standard balance connectors.