Try Right-click (or press and hold) the volume icon on the taskbar and select Sounds.
In the Recording tab, select the microphone. Select Configure.
in the last tab there is an exclusive mode for the audio behavior. look if there are both ticks set.
in the tabs before you could also check if everything is right.
maybe your 3rd-party-software mixer will also have audio settings. something can remain activated even if you uninstalled the software .... so if you have used the manufacturer mixer in windows you should look if you can adjust audio behavior / phone mode there.
same here.
that sounds like you have totally bent the mixer settings. maybe you should uninstall the sound card correctly (also in the device manager), reboot, ccleaner run over it, reboot and have a clean install.
exchange monitors, cables or graphics cards (against each other) ... if the error moves, you can make out so which part has a defect.
By the way, 5760 x 1080 is a cool idea ... I never thought about trying another ratio.