2 things you need to do....and 1 thing you need to keep in mind...
The 1 thing you need to keep in mind: From my experience, Edirol Orchestal can only have 4 different output tracks to the FL mixer for each instance of the "Edirol Orchestral" vst in a channel.
1st thing you need to do: Click on the "gear" icon in the upper left corner of the Edirol Orchstral plug-in window. Click on the "processing" tab. Then set the Orchestral 1/ Orchestral 2 box to --. Set Orchestral 3/ orchestral 4 to 1, set Orchestral 5/ orchestral 6 to 2, and 7/8 to 3.
2nd thing you need to do: Set the outputs of Edirol orchestral accordingly: click the "output" button on the right side of the Edirol Orchstral plug-in window. Set whatever "channels" you want to be routed to the respective track....1-4. They correspond to the same tracks you just set in the processing window. 1 = 1/2. 2 = 3/4. 3 = 5/6. and 4 = 7/8.
So depending on which track in the FL mixer you route the main "Edirol Orchestral" channel to (in the upper right corner of the FL channel window, the box labeled "fx"), it will take up that one plus the next 3 on the FL mixer.
Example: If I route Edirol to track 6 of the FL mixer using this setup, the first "channel" within Edirol will be routed to track 6 in the FL mixer, the second "channel" within Edirol will be routed to track 7 in the FL mixer, and so on...Edirol will occupy tracks 6-9 in the FL mixer...
But like Wedges2 said, in order to utilize those extra tracks you need to create "MIDI Out" channels in the step sequencer that have the same MIDI port setting of Edirol. So to use each of the 4 available outputs of Edirol you have to add 3 MIDI Out channels.
You will probably want to save a separate "performance" file for each FL project/beat you are using Edirol Orchestral in, because it doesn't save your instrument selections or modifications with your FL project (in the Edirol main plug-in window, click the "system" button on the right side of the window, then next to "performance", hit save.) Every time you load up that project within FL you will also have to load the Edirol "performance" file to get your instruments and outputs back.
Peace!