Hi,
It is not possible, at least directly and in a general way.
If you are playing tracks stored on your Android device, you can do it using
an Android music player app that support crossfading and using the 'Audio Cast'
feature of BubbleUPnP to capture the audio of that music app to stream it to your renderer.
'Audio Cast' requires at least an Android 10 device and a third party music app that supports being captured (most of them do).