I am having the same problem with my HDHomeRun Prime not showing up in MC21's TV devices. Even though I have followed the recommendations in this thread and the links provided here, I haven't been able to get this to work.
1. I have run the setup wizard multiple times. It identifies my HDHomeRun Dual ATSC Tuner, but not my HDHomeRun Prime. The list of devices is blank when I select 'Digital cable or satellite' as my device and 'CableCARD' as the tuner type.
2. My HDHomeRun Prime software is installed on this PC and works with the HDHomeRun VIEW program. In other words, I can view TV from both the HDHomeRun Dual and Prime on this PC with the VIEW program. I don't run Windows Media Center on this PC, so it has not been configured. This PC is normally a headless server located in a closet. It is connected to our whole house audio system. It serves a couple other PCs. The other PCs also run WMC, but I use MC for listening to music and watching movies. I am testing to see if MC21 is a viable replacement for WMC for watching TV. All of my PCs run Windows 7 and my cable subscriber is Charter Communications and the only channels they flag as 'copy once' are the premium channels. Since I don't subscribe to the premium channels, theoretically, MC 21 should work with my HDHomeRun Prime. BTW, I was told that since my other PCs always load the server's library, I need to setup the TV feature on the server before doing so with the clients. So I connected a monitor to the server instead of working with it remotely with Window's Remote Desktop Connection, like I normally do.
3. I made sure my Windows firewall allows MC21 access through the firewall.
4. I have enabled the option "Use Media Network to share this library and enable DLNA". This feature works fine with my movies and music in my library.
5. WMC has not been run on this PC and none of the WMC related programs are listed in my list of processes in task manager. However, the ehRecvr service is running and I am not allowed to stop it.
6. The HDHomeRun Prime does not show up in the "Tools/Options/Television/Manage Devices" dialogue.
7. My HDHomeRun Prime does not show up under Window's Device Manager list of 'Sound, video and game controller" devices. HDHomeRun DMS 13106531 is not in the System devices either. Like kieran mentioned, the HDHomeRuns are not local devices. They are connected to the network, so they probably should not appear under Device Manager.
However, HDHomeRun DMS 1310651 is in the MC21 list of libraries. I downloaded, installed and ran 'Device Spy' and it appears 3 times:
HDHomeRun DMS 13106531
HDHomeRun DRI Tuner 13106531
HDHomeRun RUI 13106531
8. The "DLNA Controller (control other devices)" checkbox is checked under Advanced in Media Network options.
Any help would be greatly appreciated.