Reply to Mashup theory - how do the good ones do it?

New into the world of production and DJ'ing ... having a blast with the DJ'ing part but mashing up songs is getting me beyond frustrated.

I have a rather simple question. How do the good ones do it? Such as 3Lau, kap slap, white panda, etc...

Are these guys acquiring multi-tracks to new and popular songs to mixdown together, or are they doing it the hard way (filters and whatnot, to get that one sound out of an MP3 or WAV).

Just asking, because I've been trying through several different VST's in ableton to try to filter out sounds myself, and have largely been unsuccessful in seperating drums, leads, vocals, etc. It makes me wonder if i'm just spinning my wheels, and somehow theres a source of multitracks for songs I can get.

Thanks for any help