MEL is different for each certified type with some differences based on specific airlines. As the pilot (i.e. final authority for the safe operation....), you can ask (demand) to see the one that applies to your airline/aircraft.

As for evac systems (don't quote me on this), absent a PA system, there has to be a (certified) way to signal the initiation of an evac. I've seen some airlines get battery powered bullhorns approved - but the key is it must be specified in the MEL.

Bottom line. My MEL is different than yours - use yours.