I recommend an airmax. Most of them have a range of 10-20km, and they won't break the bank too much.
Motu has Cat-5 AVB network audio interfaces. The 8a does 8in 8out, they also have 16 and 24 channel models.
It supports windows and mac, and supports USB and thunderbolt too.
I have personally used these products, they work well.
You install the Motu software on the PC, use say JRiver or Foobar for the player.
Two wireless directional dishes or linked antenna's.
You can control the Motu via any browser, be it a phone, tablet, laptop or PC.
For controlling Jriver and Foobar, you'll probably need to use a Remote Desktop software, such as Chrome RD or TightVNC etc etc there are many.
You'll need a power source on the hill, be it a puresine genny or an underground 8awg power cable.
You'll of course need an amplifier, like a Emo A-800
and the needed TRS to RCA cables, which are cheaply found on monoprice, amazon, parts express or sweetwater.
If you aren't a fan of wireless, the Edgerouter supports 1Gbps fiber for $79 (you'll need two, plus the SFP fiber cable to go up the hill.)
There are many ways of doing this.