Yes, perhaps your way work; but he needed to have both audio track separately, by this way he can change volume, effects ecc. for 1 track (for example the mic) and not for the other (the PC audio).
Ok, try this workaround: 1) preset the Youtube 720p preset; 2) in the same tab go to settings; 3) new window: "Format settings", first 2 lines: "Fit Height" and "0 x 720"; 3) try to change 0 x 720 in 0 x 1080; 4) in FPS field change "30" with "60" 5)...