It might not be the channels itself, rather the signals aren't processed correctly out. So, if we rule out any (miss)configuration:

Have you always had this and it was there from the moment you built the pc?

Try testing with some high quality surround sound or equivalent. If it happens to those two games only and not in other games, movies or even music, then most likely it is a problem with those games, or their sound files/output. I don't know those games personally, so I can not comment on what sound api they use. Some games implement different types of "engines" with various degrees.

Try different versions of soundcard drivers. If the problem exist in other games, movies, soundfiles, then it could help downgrading the drivers. If that doesn't help then the problem might be hardware related, aka the mamaboard or speakers. Reverted cables will not cause it to skip the higher end of the sound image (that's how I interpreted it).

Test the speakers on other sources/computers. Just to rule them out of the equation. Maybe at a friends pc...

Re-format and reinstall windows 7/8 (and get rid of win10 altogether)

Check you own hearing - you might be older than you realize :p

Have you tried other surround audio sources than those two games?

These audio files should allegedly be multichannel and will speak the channel they're supposed to go through (though my computer only have stereo audio, so I cannot accurately test that they actually work).
If you hear "Front Left", "Centre", and "Front Right" loud, it should be all-right, and the games are wrong. If you instead hear "Surround Left" and "Surround Right" louder than front, your setup is somehow reversed.

Maybe you have some sort of "sound manager" software; and it is "set wrong" for your setup.

Ref. attached for what's on my system, for example.

On that, if I "set" if for an incorrect "Speaker Configuration" (such as "5.1" when I only have "Stereo"), then perhaps it might have the symptoms you describe.

I haven't tried that - because I don't want to chance "messing up" my system - but maybe it's something to check into..?