There's a simple solution to "shut everyone up" - just DELETE the corresponding files.

I dunno why in 2 years nobody on Steam, GameFAQs or Reddit came up to this simple solution.

For battle voices, there're no mods at all.
For navi, there's a mod on Nexus which sadly only removes Mimi but not the other Voice late in the game.
There's also a mod on GameBanana which requires complex install (original mod deleted due to some "copyright" thing).

If it breaks smth else, please mention it in comments. I didn't do much playtesting of this method. So far everything works fine, only 1 boss battle didn't start (but another did).

To mute navigators, go to:
steamapps -> common -> SOUL HACKERS2 -> SOUL HACKERS2_Data -> StreamingAssets -> Sound -> VOICE -> Jp (En)

Backup file MAP_COMMON.awb to a different folder and delete from original location.
Only delete that file, do not touch .acb file with the same name.

Save before important events ("You feel dangerous presence"). In case Boss battles won't start, restore the file.

To mute battle voices, go to:
steamapps -> common -> SOUL HACKERS2 -> SOUL HACKERS2_Data -> StreamingAssets -> Sound -> VOICE -> Jp (En)

Backup file BTL_COMMON.awb to a different folder and delete from original location.
Only delete that file, do not touch .acb file with the same name.

Save before important events ("You feel dangerous presence"). In case Boss battles won't start, restore the file.