Maybe this question can't be answered yet, at least, not until Android M is released and on TV boxes (like Nvidia Shield)

How capable is Adoptive Storage? It probably works great for a single external hard drive connected, but what about 2 or 3 self-powered external hard drive connected on a USB hub, also self-powered? Or what about multi-bay hard drive enclosures?

Media files are huge. It would be great to have a way to expand storage as needed...