Ok so I seem to have sorted drm. But now I have a hundred or so files that say (in google music manager) no music in file but the few I have checked are all present and correct.
It's been some time since I did it, but I think I deleted the songs then redownloaded them using the iCloud icon *in the library* rather than going into the store. I'm not certain though.
I haven't done it yet, but so I may be a little off, but first set your "View" settings to "Show Music in the Cloud". Then you should see the songs come up with that little cloud symbol after you delete them off your hard drive.