I don't know any easy/elegant solutions for this. I don't think any of the models mentioned above support alarm out or audio out.
IMO what would be easy (but not really elegant) would be to setup
Blue Iris on an old PC. Blue Iris can do a bunch of different things when a camera triggers, like play a sound file. As long as you can wire your outdoor speaker back to the PC (which might require an amplifier depending on what kind of speaker you're using), you're pretty much done. Additional danger here is that you'll start playing around with BI more and end up liking it a lot more than your NVR ... that's happened to a bunch of people here, including myself.
If you only needed the sound in one area, Dahua has some newer "Active Deterrence" camera models that can play sounds directly from the camera when motion is detected.
I've also seen some threads around here with
tools/scripts that people run on Raspberry Pis that connect to the cameras over the network and alert when the camera senses motion. You could probably add a speaker amplifier card to the Raspberry PI, hook up a speaker, then have the Pi play a sound when the tools detection motion on a camera. But that's a solution that will take a good amount of home brewing by you.