What don’t you like about the current options?
If it’s the volume level, that’s limited by law in many US jurisdictions to just below the level of a smoke alert, so around 110 dB at maximum. In some places you can get a license to have a louder siren. There is typically a pretty big fine the second time it goes off, as it’s considered a problem for your neighbors.
If it’s some other feature, people may have ideas on that.
As far as hacking the siren, I wouldn’t bother, personally. I just use a Contact sensor with dry contacts or maybe a relay like the Mimolite. It would be cheaper and easier than taking apart the Aeon siren. Then just sell the Aeon siren that you already have if you don’t want it anymore
If you look at the topics in the forum on hacking a doorbell, it’s the same basic idea. Here’s one that discusses several options: