I am having this same/similar issue.
I am using two laptops running high DPI displays, both having the same issue, both running Windows 10 PRO 64bit
One is a MacBook Pro with GTX 650m - GUI display : 2880x1800
One is an Alienware R3 with GTX 1060 - GUI display : 2560x1440
EDID output resolution always shows up correctly under "device", but resolution is always wrong on the "screen" in Resolume advanced output.
In Arena 5 this issue can be fixed by checking "Disable display scaling on high DPI settings" under "Compatibilty" when right-clicking the application. (But of course you then lose the ability to scale the GUI)
In Arena 6 this fix no longer works. Just shows different but still-wrong resolutions on any scaling settings or when disabled.
Please let us know if there is any headway being made on this, as this is curently the main thing keeping me from ugrading my whole production to R6! And I really want to
Also let me know if I can provide any other information, or if there are any other fixes to try..