Ahh. Although there are tons of people who prefer to edit in H.264 on a regular basis ... though the DNxHD wrapper is excellent. It looks like one would need to download the mkv codec in one of various packs to say have it fully accepted in the PC line? Though I wonder if you've got the mkv codec loaded, if AME (the export program of PrPro) could have done your transcoding to DNxHD or perhaps Prelude).
Neil