@stevenscott I messed with it, and it's exactly what I want! Unfortunately I had to read the sourcecode to figure out how it works. So to save you the effort:
When you run the soundboard.exe, no window opens. You need to press alt+control+something, and it will open a "browse for file" dialogue. Here you can find a sound (wav/mp3/whatever) you want to play on the hotkey you just pressed. If you have other hotkeys already registered, soundboard won't conflict with them; you just can't use those keys for sounds. I have alt+control+n for NVDA, and alt+control+J for jaws, so when I press those soundboard just does nothing and they do what they're supposed to.
If you press the key for a sound multiple times, that sound just restarts from the beginning. You cannot pause or stop a sound that's currently playing. So don't press the wrong key!
If you want to quit soundboard, press alt+control+q.
If you want to change the sound on a particular key, you have to open soundboard.ini (a file it makes in the folder with soundboard.exe when you run it) in notepad and change it yourself.
If you want to change the volume of soundboard, or make it use a different sound device, it doesn't matter what you want, because you can't. For simple lads like me, that's okay. But I suspect it might be a problem for all of you complicated radio professionals. LOL :-)