At any time when using the Phorus app, or from the Play-Fi applet in Windows, if you want to add more speakers, just press the Play-Fi icon. In the apps, the icon is in the bottom right side of the screen, and in Windows, it appears in as a system icon in the lower bar. The list of speakers will appear. Simply tap on any speaker and it will be added right away, even if you are in the middle of streaming a song. You can add more speakers, control individual volume levels, and remove speakers, all from this speaker screen. Make any changes you like, but if you remove your original speaker from the list, the music will stop.
To create a shortcut to a favorite set of your Play-Fi speakers, use the Groups tab to place speakers into whichever combinations you like, and give them a name for easy access in the future. Speakers can belong to more than one group, so it’s easy to have groups like “All”, “Upstairs”, and “Party Rooms”.