Your asx does not contain streams but a playlist. Anyway it does not play it properly nor does it play the asx files it can create. You can create playlists in m3u, pls, mpcpl and asx format from within MPC by using view/playlist as you may not have noticed, and then you can right-click on that playlist and choose save as. You can use any of the other playlist formats as they all work for playback and fill a bug report to Gabest so maybe he will fix this in the next release, as it would appear to be a bug.