João Dias I made a BubbleUPnP AutoShare intent that will turn on "Audio Cast". Can you add this to the list of intents?
https://www.dropbox.com/s/fgyjcki7hyep92e/bubbleupnptoggleaudiocast.intent?dl=0

Note: Root needed + BubbleUPnP Xposed Module + foobar2000 UPnP renderer component 
http://www.foobar2000.org/components/view/foo_upnp

Here's an example task to demonstrate how it's used.

BubbleUPnP (200)
A1: AutoShare [ Configuration:App: BubbleUPnP
Action: Start Service Package:com.joaomgcd.autoshare Name:AutoShare Timeout (Seconds):10 ] 
A2: Wait [ MS:0 Seconds:7 Minutes:0 Hours:0 Days:0 ] 
A3: AutoShare [ Configuration:App: BubbleUPnP
Action: Toggle Audio Cast Package:com.joaomgcd.autoshare Name:AutoShare Timeout (Seconds):10 ] 

Launch the Spotify app and play something. The audio should playback on your PC with foobar2000. 
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