Firstly you will need any sort of extracting software that you can use.

In this guide I will be using 7-ZIP for the extracting part.
If you wish to install 7-ZIP click here.[www.7-zip.org]

Firstly, in order to access the game's original files, you need to browse local files on the game's library accessed by clicking the gear icon on the right.
Most of the game files are located inside the .EXE game file, in order to see what's inside, we can use our extracting tool by opening up the archive.
In order to do that, proceed to right click the .EXE file, hover over 7-ZIP and then click open archive.

Now you should be greeted with the archive of all the soundtracks in the game and other thingy majigy stuff.
Firstly you want to select all the soundtracks that are labelled with music_ and click the extract button at the top of the window.
Once you click the extract button, you will be shown a window on where you want to extract the selected files, you can either let 7-ZIP extract the files where the .EXE file is located or you can set a custom file path by creating a folder anywhere on your computer and copying the file path and pasting it.

Once you did everything correctly you should have all the original soundtracks extracted out of the game, happy listening!