Jajaa~n, it's all mixed! :D
Go listen to it here: http://www.4shared.c...tar_Thea_.html?
The parts were divvied out following the original lyrics (http://projecthello....noudedokei.html), and the parts are as follows:
Star - Reina
Thea - Riho (and Reina's first few lines in the second verse)
arco - Risa
tangerine - Aika
There's a few iffy timing errors that I wasn't able to fix, but otherwise, it sounds pretty decent, so go check it out if you want~