Most of the streaming services encrypt their downloads to prohibit exactly what it sounds like you want to do. Kind of a bummer, but I suppose they need to protect themselves in case you download tunes then cancel your subscription.
Google Play Music doesn't (I think), but I'm not sure if it's the quality you're after.
Not sure what else to suggest unless you're looking at paid stuff for free (piracy) buy you'll get no help with that sort of thing here.