What are the best affordable outdoor monitors for the Sony STR-DH190

[Nerdtendo]

I'll preface this by saying I know very little (read: nothing) about audio hardware. My dad's been wanting an outdoor sound system for a while, so I picked up the stereo (a Sony STR-DH190) for father's day. We're sitting on an acre of land, and my dad wants at least two monitors that can cover the whole yard (one in front, one in back). These are his criteria

- can withstand rain, heat, and cold

- are hard-wired

- relatively affordable

- loud enough to each cover about half an acre without sounding too grainy.

 

Most options I'm finding online are wireless which isn't really what we're looking for, and I'm having a really hard time figuring out where to look. Any help would be greatly appreciated.