you don't need a second drive, just another partition for your media since it will be written to. otherwise you'd have to worry about disabling EWF before copying new media over. if you have a writable drive then you can easily add music to it without worrying about the EWF memory layer taking up all your RAM.
there's one issue though....if you plan on using HORM you may want to consider getting a USB drive you can unplug before creating your hibernation state. Microsoft recommends doing this to flush out the write cache for the media drive. Otherwise the write cache will be persisted with the HORM state and be present every time you boot up, possibly corrupting your drive.