I just wouldn't, especially on a modern panel with more options. One zone per device, so you can diagnose any problems.
Your sketch seems alright assuming it's DP, time to get the multimeter out take everything apart and work out what's going on.
Been given 2 of these, both new but tatty boxes
Before I consider them as WEEE I thought I'd document them for the nerds here.
Didn't find much info on them from searching.
Most wired sirens are compatible with wired systems but keeping the same manufacturer means you are likely to have instructions for how to connect there own.
Have you proved it's actually the siren at fault?
Having listened to the podcast already it's not related, images came from social media.
It will take a defence lawyer to get the evidence thrown out on possible deepfake grounds, for change to happen.
If you handle evidence properly with decent kit it shouldn't be an issue.
IXP is for third party kit.
IProx can't be wireless so I don't see why keypad would be, also a wireless keypad will depend on what other wireless equipment you fit as to if you have capacity at the expander.
I'd be surprised a house with a flush keypad fitted would only need 3 sensors...
If your having a company in it's no good recommending kit, they will use what they support.
If you found somewhere reliable that supports Galaxy then less repair work.
Usual recommendation is 3 quotes, go with the place that makes you feel the most comfortable NOT just the cheapest.
There can be unforeseen planning permission issues and they are unnecessary light pollution.
You can fit them without connecting the backlight on the X's, but can purchase the twin siren non-X ones for similar price.
Covering a new box with what I guess is some old C-Type cover would remove the deterrent of a shiny new box and reduce sound output.
If you are thinking of not buying a lid for this sounder it just will not work, they need a compatible lid.