I'm just in awe of anyone who can put sounds together like this. I am totally impressed.
Honestly, it's not as hard as it sounds. Time consuming? Absolutely. Tedious? Definitely. All I'm doing is collecting a bunch of sound loops I like together and auditioning them next to one another, moving them here and there, time stretching them, matching them to the chord track of the song, and then applying fx when I get a combo that I like. If I want to hear a special instrument here and there, I go hunt one down and audition the loops while the song is playing to see if it's a good pair. It's a wonderfully useful feature of Studio One.