I think a number of us have experienced Media Streamer hanging when we use it as a media controller. This happens to me all the time with my 770, Roku Soundbridge M1001, and TwonkyMedia. I filed a bug report at maemo.org yesterday,
Let me put it to you then: Does your N800 hang when you use MediaStreamer as a UPnP controller (e.g. to control the playlist on your Roku Soundbridge)?