Actually, I think I just got it.
What I did above might have worked but I didn't leave it alone long enough. Regardless, the following is working... 1) Move your "My Music" folder by finding it in your user account, right-clicking, choosing the location tab and then move. You should
let it move all the files when it asks. 2) Go back to your My Music folder in your user account, right-click, choose location again and then move the folder back to the original location. You'll probably have to create a new folder in that original location
named something like "Music" or "My Music". Regardless, this time do NOT move all the files. This will (eventually) clear out your Media Player library and you'll have a clean My Music directory. 3) Now, copy a few of your artist/album directories from
where you moved the original to into the new cleaned out My Music folder - note that I didn't find move to be as successful. If you have Media Player open when you do this they will add right back into Media Player. 4) In Media Player chose Organize and
Apply Media information. 5) Finally, when you choose the streaming options they'll appear on your Xbox. At least they did on mine. If all that works and you can see the files you just moved on your Xbox, go ahead and do it for the rest of your music.