Onto the good stuff now: as some of you know, noted modder Looyh released his NBA 2K Music Converter tool, which allows us to change any track on the in-game soundtrack - and maybe arena/crowd audio as well, although I don't have the necessary modding skill and/or experience to confirm that.
Step one: add all your .mp3 files into a specific folder by themselves.
This may seem oddly specific, but it greatly speeds up the whole process. (Tip: many media players, like MusicBee, can export the songs off created playlists into a folder.)
Create two folders: one for your unedited .mp3 songs, and one inside it (or wherever else you'd like to) for the edited .mp3 files.
Step two: once they are there, add a batch of them (max 10-15 at a time) into Audacity.
There might be other audio editing suites for that purpose, but Audacity is the most practical one. Once you've downloaded it and opened the app, press Ctrl+A and go to Transport -> Cursor To -> Track Start.

After this step (and while the cursor for all tracks is at the beginning), go to Generate -> Silence. Once you are there, select the preferrable type and type in one second. This is done in order to ensure that the beginning of each song is not skipped by the conversion.

Step three: after one second of silence has been added to each and every track, it's time to export them.
Go to File -> Export -> Export Multiple.

And while you're there, select MP3 as the format and the EDITED TRACKS folder as the extraction folder.

Several windows will come up, press OK at them all, and wait for the extraction process to end.
Step four: after this is all done, open up the Music Converter Tool.
Press 1+Enter for English. After that, drag and drop the EDITED TRACKS folder into the command window, and press Enter. This will convert your files into .wav format inside the edited tracks folder.

Step five: when the .wav tracks are inside the folder, drag and drop them into the ...NBA 2K20\waigua\newaudio\jukeboxmusic.
If any of those folders isn't there, create it. However, 2K20 won't read the tracks until you've renamed them. Rename every track as 0000**-000000-000000-000000-000000-000000.wav with the asterisks symbolizing a number from 00 to 74.

In the end, this is how your folder should look.
Hope that helps a few people. Have fun out there and stay safe, everyone!