By default your OpenVoiceOS device is advertising itself as Airplay (v1 - currently) device on your network. This can be used from either the iOS Airplay selection screen if you play some local files, like shown below; Tap / Click the bottom middle Airplay icon on your music player which opens the Airplay devices menu. It should pick up your OpenVoiceOS device automatically from the network. Select the OpenVoiceOS device to re-route your sound output to your OpenVoiceOS device.

The Airplay selection menu is also available within other music clients such as the Spotify app. And if that client also supports metadata over MPRIS your OpenVoiceOS device will show it on it's screen as well.