Oh I see! sorry. I'll give it a try.
No probs.
If you want to go the route of lowering your resolution to hit 75Hz on your monitor then just Right click on your desktop, select Screen resolution.
Hopefully you'll have your DK2 in extended and you'll be able to see two (or more) displays in there, one being your DK2.
Select your monitor and drop the res by one notch on the slider.
Click Advanced settings>Monitor
And check the available refresh rates.
If it is only 60hz still then back out and lower the slider another notch.
Repeat the process till you find the highest res you can run at 75Hz.
I'm not 100% how I did it but when I turn my rift off using the little button on the top my monitor resets back to 1440p at 60Hz which is great as it saves faffing about. Turn the DK2 back on again and it resets the monitor back to low res 75hz.
The only issue you'll find with this is when windows and stuff are on the Rift as it's hard to see.
You could try virtual desktop which fixes this issue (but not sure if it has an overhead) or dragging stuff over to your normal screen (which works most of the time, the UE4 launchers never seem to want to move though).