It worked! Sort of...
I enabled MC as a DLNA renderer and am able to stream from my tablet to my PC using the Android app 'BubbleUPnP'.
But, like you mentioned, so far I can't relay the audio from my apps (TuneIn Radio, Pocket Cast) to the output of BubbleUPnP. I don't care about streaming my MC library to my PC, I've always been able to do that and I can even control it with Gizmo if I want.
To get BubbleUPnP, you have to pick a rendering device and a library. I've set the rendering device in BubbleUPnP to one of my MC outputs. Under the libraries I can choose between the media shares that it finds on my network or from the libraries on my Nexus 7. So the only media shares I have are the ones that are enabled in my network settings that stream using WMP. Since I haven't imported my music collection into WMP, nothing appears except a couple sample files (BTW, last time I added my music collection to a WMP library, it messed with my tags, so I don't want that to happen again. Besides MC is much better for music playback.). I'm surprised that the local music on my Nexus 7's 'Google Play Music' app aren't appearing on the list of local device libraries.
It would be great if I could set it to grab any audio that is played from the Nexus 7, but that doesn't seem possible.