I know Nexus has alot of choir single pads that sound alot like what you guys are looking for. http://refx.com/
I assure you, that you'll find what your looking for using that vst
If you want to make an "ambient synth" just create ambiance . For instant if you wanted to make a pad: turn the voices up on a synth lead, raise the attack and up the release some & add some fx . That's a way to get a quick result but there are other ways . There's no specific hardware or software to do this because all of them can do it .
Try using synths and then turning down their attack. Also, try using Maj and Minor 7th chords with the added 9. Experimentation is really the way you are going to get the sound you want. Nobody can tell you exactly which buttons to press or what programs to use.
you could easily layer a pad with a choir,just turn the choir down a bit & have the pad louder than the choir."The Calm" to me sounds like he layered a pad with a muffled stuttering choir & distorted ass hell(thats just me though).