I have one computer that functions as both a media computer and a workstation. Attached to the computer are two display , a 1920 x 1080 plasma TV connected via HDMI and a 2560 x 1440 WQHD monitor connected via DisplayPort. Also, there is an AVR, the monitor has speaker and I also have headphone. I live on the edge of a HDCP violation and I think you are right to think you have a HDCP issue. Last night there was a storm that momentarily cut power while both displays including media center were running and on the plasma I got the following message:" Video Error Files needed to display video are not installed or are not working correctly. Restart Windows Media Center or restart the computer."
Restarting media center nor restarting the computer resolved the problem even after multiple tries.
This morning I stripped the system down the monitor running at 1920 x 1080 and a set of headphones connected to the computer and got media center working again. Then I added the plasma and AVR back in and then media center was working on the plasma again.
I have never tried the Shark007 codecs because I have gotten the system working the way I like without the codecs. But from reading Shark007 seems knowledgeable and many use his solution.
But what I wanted to say is that HDCP is a scheme the content producers created to protect their content along with the protected audio path. The software and equipment manufacturers built software and equipment which can play the content as long as the user keep his or her system simple. However, you with your extenders and me with my two displays and two audio sources live on the edge. When I fall over the edge and my system stops working the way I want I begin striping the system down to one computer with one display and one audio playback device. Once I have it working again I add everything back and it usually keeps working until the next unknown issue occurs.
So, what I am suggesting is to first try simple solutions others suggest. If the simple solutions don't work try simplifying your system until it works and then build it back up.