I had seen that mogg hosting site. Was going to take a while to download them. Several rar files to manually click for each letter of the alphabet. Looked around reddit for multitrack files, found r/songstems then sorted by top posts. Noticed this guy hosting a nice library.
https://www.reddit.com/r/SongStems/comments/1vqwj2/i_got_more_stems_than_ive_got_gray_hairs_and/
Problem trying to download all the rars. There's 2 hosting pages of the alphabet. The first section was able to download the zip. The second part, it would crap out. Noticed you can also download them one at a time. That worked. So if you're going to get those, select the one at a time option.
Looked around for more. Checked pirate bay torrent for "multitrack". Got the 20 part "The Largest Multitrack Music Collection Ever! (2013)". They're about a couple GB each part.
Got another torrent that was 4GB. Combined all 3 libraries and then went thru them checking for the higher quality verions to get all my files.
I'd open them with audacity. A .mogg is one file but there's no pan information and you have to figure out what goes left and right. Gets tricky when some things are mono. Often the kick drum and bass guitar are mono only. You'd get some older song vocals where parts are mono.
Most of the time the source files would just be .ogg in a folder and if you'd select them and drag into audacity, they'd be stereo. So those would be fine. It's those damn mogg ones where you have to figure out pan. Some of the 60's material, if it was instruments in full left or right and the source file was stereo, I'd leave it like that. But if it was a mogg and mono, I'd sometimes even things out a bit by putting it a bit in the other ear. For example, Queen's Bohemian Rhapsody, I think there was 20 vocal tracks but all mono. Don't want that all mono, and didn't have time to check what official verions do so just kind of put the pan wherever instead of mono. You check what's going on and try and do something with the left and right instead of mono or buring in one ear.
Then for all these 5 versions per song, I'd go along and mute tracks then export them. Solo wasn't working so had to do mute. The versions were [normal song], [mute vocals], [mute drums and mute vocals], [mute drums], [all mute except vocals], [all mute except drums].