Airplay doesn't work with B&O Airplay devices

Pretty simple issue, actually. Many B&O devices support Airplay, and work fine with Apple sources (iOS or OS X/macOS).

I’m running Roon on a Synology 2415+, and while it works with “real” Roon devices (e.g. an Auralic Aries), it isn’t working with Airplay to these units.

They’re seen, and you can select them, and put them in the queue, but actual playback never starts.

Being a new installation, all options are set to their defaults. The source is an ALAC lossless that requires no transcoding.