Hello hello! My first post, but I felt inspired because I finally figured it out. I was having the exact same problem, same Realtek drivers, etc. My solution isn't perfect, but it'll get you the audio you're trying to get in your rift headphones. I do hope this helps, but apologize in advance that it's not "perfect."
1) Open your playback devices, set your rift headset as the default device.
2) Right click on your Rift audio device, and select Properties
3) Select the tab that reads Advanced, and change the drop down to CD Quality. (I believe the default is DVD quality.)
4) Open your Oculus Software. Select the settings Icon in the upper right. (Looks like a gear.)
5) Select Devices on the left, then select the headset. In the "VR Audio Output" change it from Rift Headset to "Windows Default."
6) Launch your game.
Hopefully this works for you. Just as a side note, I only recently figured this all out and one thing I noticed as I type this out is when I exit the game (Skyrim, in my case) windows resets the default speakers from Rift to Regular Speakers, so it seems you might need to set the default headphones as the rift every time you want to launch a game. I hope this fixes your problem. Please let me know! Good luck everybody.
