I have a mothballed RX-S601D in the eaves cupboard with four years of dust resting on its lid, the awfulness of Yamaha's AV Controller and MusicCast Controller apps part of the reason I gave up.
At the time I chucked it into the cupboard it all felt too half-baked and proprietary for my liking, and looking at the two app stores today I'm really not sure much has changed. The Yamaha duo remain some of the worst rated big name apps you can download: the former last updated pre-virus and the latter having the cobwebs blown from it when iOS 14 appeared in the summer.
I have to confess that from investigating and tinkering with the competition they ALL fall strangely way short of what I would consider ideal. Strange because the accompanying hardware is so expensive. You can't help but wonder if owners really are more interested in look rather than feel.
Speaking of such, the B&O app does feel like the B&O team are at least trying to keep things on the boil, whereas the Yamaha apps are terribly rated (both are 2-star with exasperated reviews) and something of a disincentive for anyone thinking about what to buy in the sales!