Given Adelaide Oval has 6-7 sirens across the old stands compared to the 1-2 at most suburban grounds, you'd expect it to be louder.
Perhaps the SACA should put in a proper PA system (not 6 speakers on top of a fuzzy video screen), and hook the siren through that. If AAMI Stadium and Coopers Stadium (even Broadspectrum did it for a while) can do it, why can't Adelaide Oval.