OK, now we might be able to make some progress. You may have to research some thing as I have not used Win8 on anything but a Surface, so not much to do on it.
Make sure all of your Laptop sound is turned off and route everything through your DP. This is where you want to monitor. You should be able to set this in Windows. It might be a pain right now, but after you get it working, you can worry about the convenient factor later.
Make sure, in Windows, everything routes to your DP. Once you hear sounds routing to your DP (Youtube, system sound etc) then go back and with either monitors or using the DPs output, fire up Reaper and give it a test drive.
