Are you not able to control multiple Air Play devices at once from an ipad or iphone like you can from a computer?

I have two Airport Express units connected to two home stereo units, one indoors and one out in my garage. From my laptop I am able to select and control the volume of both devices and have the same music from my itunes streaming through both stereo units. When I try to stream my music from my ipad or iphone, the Airplay feature won't allow multiple devices to be selected at once. If you select one Airport Express, it shuts the other one off. Is it not possible to control and have all Airport Express units play simultaneously through my phone or ipad? I am running current versions of iOS