I am using a combination of the following to achieve what you are asking:
- Generic DLNA Media Renderer
- UPNPlay Android app - Launch the app and select Android Player as the device. Only after doing this, it would show up in SmartThings DLNA app.
- Sonos Notify With Sound smart app - available from marketplace.
Currently, Sonos Notify With Sound allows only very few notification sounds (bell, laser etc.). I would like to change that with some other notification sound. Is that possible, may be with another smart app?