I always use DVI mode on my HP 1600×1200 LCD monitor, which only has DVI inputs, or else I don’t get any video at all out of the OSSC.
I use HDMI mode on my Asus VG248QE 1920×1080 144Hz TN monitor. Line5x doesn’t work on either of those two LCDs.
I have set the correct Line5x formats, 1600×1200 for the HP and 1920×1080 for the Asus, and saved it to my settings for each monitor.
My only display that works with Line5x is my 19 inch Daewoo LuComs C925DBK VGA CRT monitor.