@Riles, you're correct, but I'm not sure how to add a volume attribute (way beyond my experience level)...but here's the way I'd do it. Don't be discouraged by all the reading, once you get it down and have a working example (and the tools downloaded and installed) its not too hard to add/modify a game sound.
To do this requires a little bit of work and may be frustrating if you haven't done it before (have to install tools, probably have to read up on how to use them a little). You'll have to extract the game sounds (I believe people still use the UABE tool: https://community.7daystodie.com/topic/1871-unity-assets-bundle-extractor/ ) then for each sound you want (You'll to search a bit for them in the assets files, they're just .wav files when extracted by UABE) , load each one you want to modify into a sound editor (maybe use Audacity, or choose your favorite ) then adjust the volume levels and re-save the sounds as .wav files. I made a sound modlet and I just extracted *all* the game sounds and then went through them vs extracting one at a time.
Then you have to get the .wav files into unity just so you can get unity to export them in the proper format. This post should help:
adding a new sound
On page 2 I made a very large post about how to add a new sound and some of the issues I ran into. But the other posts are good for learning the process. Its actually relatively easy once you do it once. I found the hardest part was figuring out which version of Unity to use, and figuring out what export script I had to download and load.
Once exported into the unity format, then you can make a modlet to use the XPATH commands replace the sounds. The modlet should be really small and easy. Here's my modlet that "adds/appends" new sounds as an example, so your XML/XPATH would have to be a little different to "replace" them:
Doughs-Buff-Sounds-Common
There's more XPATH tutorials in the forum here:
tutorials-guides
A good one to start with looks like:
xpath-modding-explanation-thread