I'm glad you're having fun with it! There's no way to set sounds to a combination of buttons (e.g. CTRL+S) by modifying the unsupported, undocumented AudioSets.json sound configuration file, but here's a potential solution you might want to explore for key combo stuff in general:
1. Download and install AutoHotKey: https://www.autohotkey.com/, which lets you define special actions and macros that happen for key combinations, or redefine keys. It's very powerful.
2. Create an AutoHotKey script that plays a sound file or beep when a specific multi-key combo is pressed. (See the SoundPlay command and SoundBeep).
You'd add something like this following line to your AutoHotKey script to make it do a low beep when ctrl+s is pressed:
~^s::SoundBeep,100,10