Steam audio without TV on

I'm sure this has been asked before but I can find a good (as in "correct") answer.

I have a ATV 4K. It's connected to my amp via HDMI. The amp is the hub receiving A/V from all devices via HDMI then sending output to TV (HDMI) , speakers etc. Basic and simple stuff.

I have a Mac Mini with iTunes / HomeShare running and we use it as the source to stream audio from our collection as well as local copies of digital downloads like movies etc. Again, basic and simple stuff.

The problem is if we're playing music from our library -- and we turn the TV off, the ATV stops/pauses the stream! If the TV is turned back on, and we push play on the ATV, music continues.

I don't want to have the TV on just to listen to music. Why is this happening and how can I get around it?

Thanks