that +1
With the SRAM 1x derailleurs you can't use a double; there's no pivot aka parallelogram.
The only one you can mix and match any longer in the current product line is the GX, X0,XX 2x10 Exact-Actuation with the 22 gear Exact Actuation brifters. This only matters for gearing > 32T when you need a long cage derailleur. You can make it work but you'll need a longer B screw to make the 11-speed cassette work. You can try and get an X9 to work too but that was more suited for the 10speed. That said the X0 and XX are splendid 11-speed derailleur long b-screw swap out not withstanding.
It looks like the days of mixing and matching mountain and road stuff are almost over. But that x-shifter electric stuff might be one way to solve it. The other way is to get a ratio adapter from Jtek which is very reliable for solve these combinations. You would what the Shiftmate 9.
http://www.jtekengineering.com/shiftmate/shiftmate-9/ That would allow you to use Apex<-->Red brifters with a 1x11 setup and a 10-42 cassette.... When I get around to building an S40 that's how I'm doing it. Eagle + Brifters