How about a network test of some mp3 audio files. That should tell you the process is good.
In my tests, mp3 and jpg files do stream successfully from the router to the Roku, so the basic DLNA functionality is good. It's just video files that are a problem. From other discussions out there it seems that it is the router
that is mis-identifying the MP4 videos as audio files. But I've not yet been able to isolate the source of the bigger problem, that I can't successfully stream video files (at least the MP4/M4V files that I've tested) even when they are correctly identified by both the router and the Roku. I am going to keep testing with other video file formats, but I've got a bad feeling that this isn't easily fixable.