The only "apps' I know of to control audio is for streamers. You can have internet radio, streaming services and all of your own music that is digitized to files.
AVR, AMP and Processor.....
My sons new home has cabling and speakers for whole house music. I also gave him my Vandersteen 2CE SIGS for his man cave. Looking for a simple solution to tie in whole house, Vandy’s, and at least 5.1 where Vandys are fronts. He will want Sonos type of convenience. At my house, I have a Yamaha with Musiccast tied to my in walls and this suffices for music house wide. I don’t do home theater. Anyone have a system that can be controlled from an app and do HT? Thank you in advance. Budget is $1K and used is fine.