Bind Volume controls to non-Apple keyboard without 3rd party software on macOS Sierra

Solution 1:

Karabiner has options that let you use the Function keys (with or without ‘fn’) on external non-Apple keyboards just like the special function keys on Apple keyboards. This means pressing F11 and F12 (‘fn’ depends on your options shown in the screenshot) to decrease and increase volume. The HUD shows as usual, and F10 works for mute too.

I am yet to see Karabiner fail to function due to an OS update, even day-one beta OS updates seem no trouble for these ‘standard’ features of the app (there's more customisable functionality which may have problems from OS updates but are fixed swiftly).

Solution 2:

Keyboard Maestro

works with macOS Sierra. It will let you do exactly what you want, it's a great alternative when Karabiner doesn't work yet. By the way, you can use Karabiner Elements instead of Karabiner, but without GUI it may be troublesome for most users.