Chromecast & Spotify (over multiple VLANs) - mDNS vs UDP Broxcast vs IGMP Proxy?

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So I am trying to get some sort of order in my head...

In my media system I have a Chromecast Ultra attached to my projector for video and TV kind of streaming. From the connection box for my projector (An Epson 9400W - wireless, thru the transmitter/connection box mentioned here) I have Optical out. The sound of that optical output goes into my KEF LSX2 speakers. Then of course I have internet radio / Spotify over coax input on the KEF Speakers. It is a neat solution I think. And it works.

My network, over OPNsense control then, is divided into separat LANs. The KEF speakers and Chromecast Ultra are connected to "Media"-Lan, over Ethernet cable - but both are also available over "Unifi"-LAN (Wifi) since that was needed to set them up. My Android tablets that so to speak control both Spotify & Chromecast are on the same "Unifi"-LAN. On top of that my Home Assistant has a finger with all this, and sits on the "HomeAssistant"-LAN. Great. Different LANs.

Now I have actually everything up and running, but I do wonder if I have created something that might not need to be there.....?

I use a combo of:
1) IGMP Proxy
2) UDP Brodcast relay
And then I also have installed, but NOT enabled, so in a way it does not count:
3) mDNS Repeater

And as mentioned, there are multiple LANs involved here: Media, Unifi and Home Assistant - that is why I need to "move" traffic between the three LANs. Yes it would be easier to just have all on one LAN. However that is not on the table currently, and after all, it does work...

Now, the question is, do I need both IGMP Proxy and then UDP Broadcast? I think one of them should be enough but I have not tried to disabled anyone of the two. Or what am I missing here?

And yes I have no idea why mDNS is installed, but at least it not enabled.... I might have in a weak moment installed it to get Chromecast to work. But then again?

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So I decided to kind of go the hard way:

I have uninstalled mDNS and IGMP Proxy - everything still works as it should.

So the answer is: If you need anything, you only need UDP Broadcast Relay plugin - it handles it all.