Reply to 4 decks output on Tr-1 mixer?

guys and dolls',

i've been trying to map my Tr-1 so that i can mix 4 decks at once. obviously two channels are already mapped out as usual...but how do i get to the other two decks (3 and 4)? i need to be able to control them individually somehow while playing deck 1 and 2...

i cant seem to work it out in the mapping. help would be much appreciated