What model TV do you have? If it doesn’t have an ARC or eARC connection does it have an optical connection?

It's an old Proscan. It doesn't have optical either.

Are you getting TV audio to the Beam now? If so, how are you achieving that?

Do you have a cable box? If so what is the model?

If the cable box is connected to the TV via HDMI, you should be able to use an audio extractor like this:

https://www.orei.com/products/2x2-hdmi-matrix-w-audio-out-2-in-2-out-ultrahd-8k-edid-bk-202a

In addition to the questions above, I’d ask: Which Proscan TV is it? 

Any reason why you couldn’t pull off the audio before it reaches the TV?

Cheapest way is to get a Coax-to-optical converter and the Sonos Optical to HDMI-ARC adapter.

Coax-to-Optical converter

Sonos Optical Audio Adapter

Proscan

Model No. PLCD3956A

I'm using a fire stick connected in the Hdmi of my TV.

If you are not planning to purchase an updated TV, which would probably be the best option, an audio extractor would be the next best thing and work well for you.

According to this page according to this page and the next:

https://www.manualslib.com/manual/821325/Proscan-Plcd3956a.html?page=10#manual

it has an SPDIF electronic output. You might be able to purchase an electronic to optical adapter that would feed the Sonos adapter that ​@jgatie linked above…but if it were me, that TV needs to be replaced before spending money on adapters. 

Thank you all for the replys!

It gives me a few options. It'll allow me to make an educated decision!