So I bought music on Xbox Music, and I can't do anything with it. What gives?

Wow, this is pretty cool - all you gotta do is go into Xbox Music on your PC, try and create a station, and it will give you a few options such as a free trial or what the OP is talking about above, which is the ability to sync your collection to OneDrive
and Xbox Music- this allows you to play your music on any device via Xbox Music. I'm currently transferring files to make this work, though, so I can't readily confirm if you can listen to music you don't own like the OP says, but if so, that would be an awesome
loophole.

Errmmm.... Can't you just play music using the Xbox Spotify app?

The music still plays through the headset. That's what I do... ¯\_(ツ)_/¯

I have been struggling with this one too. Here's what I ended up doing:

1- In the app, select ALL the albums and then delete them.

2- Wait for the xbox music app to stop freaking out. It'll give lots of errors saying so and so album failed to download. During this process, the download queue will drop like a rock.

3- Restart the music app, just to make sure there isn't anything downloading any more.

4- Once everything was clean, I turned off ALL syncing.

Now I have a clean slate, and I'm about to start copying my music back. I'm hopeful that this will do it. I'll post back here and report what happened.

The XBOX music cloud is a great concept, but there needs to be some better control over what is synced. My biggest problem was that I have a lot of ethnic music, most of them digitized from old cassette tapes. I have painstakingly authored the metadata
for all of these. When XBOX music sees these, it doesn't know how to handle it and starts replacing the metadata with the closest hit, ravaging the entire collection. While conceptually it is a good idea to have the entire music library available on any
device you own, there needs to be a global setting on the XBOX music pass subscription that gives you the ability to turn off metadata updates for all devices.

I've never had to do anything like that with music, but if it doesn't give you an option to copy or move the tracks, it's most likely to do with how the music tracks are licensed to work. Mainly to keep it so you can't copy it and pass it out to other people.
I know movies and TV shows have that kind of licensing restriction on them.

Xbox files are not meant to be seen via the PC. So you would be violating the terms of service if you were to transfer them to a PC.

I am having this same problem. With Xbox music, AOE: Castle Seige, Microsoft Bingo. It seems that anything W8 app that is trying to log in with my windows account cannot do so. Please help, this is killing me. Can't play music, can't play games... the
only thing left is just to keep working! I'm on W8.1, standard desktop machine.