FL Studio supports VSTi plugins with multiple outputs. In the plug-in window, click the down-arrow menu (upper left corner under the red plug-in icon). If the plugin supports multiple output, you will see "enable multiple outputs", select it. Now the first output will be set to whatever FX channel is initially assigned to that plug-in, and each successive FX track will contain the additional outs. For example, a plugin with 4 outputs assigned to FX track 10, takes tracks 10, 11, 12 and 13.