Then, when you add instruments to Kontakt, you need to set the output of an instrument to one of the mixer outputs in Kontakt. the 'home' mixer channel + the offset - h+0 h+1 h+2, etc.). If you put your instance of Kontakt on FL mixer channel 1, then the outputs would run from 1-8 in the FL mixer (i.e. The bottom half of this screen is called 'Connections.' This is where you configure the mixer channel offset for the FL mixer. It's not well differentiated, but there are two tabs, settings and processing. Next, open the fruity wrapper settings (when you click the cog, it's the second button, which has a plug and a cog on it). Mixer 1 -> audio out 1+2 Mixer 2 -> audio out 3+4, etc. The idea being that you set each mixer out to a pair of audio outs.
Follow Kontakt's manual for how to configure the internal channels. Next, you may need to set up Kontakt's internal mixer to send each mixer channel to a different pair of audio outputs. Select 8 out (4 stereo outputs) or 16-out (8 stereo outputs). So you may see Kontakt, Kontakt 8-out and Kontakt 16-out in the plugin database.
First, make sure you're selecting the version Kontakt that supports multiple outputs.
