the plug in windows work differently for synths and fx. firstly if you are using synthfont i would enable it as 'divert to dxi/vst sytnth in the midid river set up.

secondly i would replace the sounds with nicer ones. synthfont can take GM soundfonts and a nice one is 'timbres of heaven'. look up my post in the forum 'synthfont is silent' and you'll see how to load new sounds. mt problem was solved by updating synthfont.

so the plugin windows work differently for synths and fx. if you clik the blue track window it will show the default synth in slot 1 and if you want to use a vst or dxi fx, use slots 2, 3 and 4. but don't forget, in the mixer for misi tracks you have a knob for reverb and chorus which semds midi isntructions to the synth.

to use a different synth for a track, select the track and it tuens red. right click and select 'specific vst/dx syth for midi track. then you'll get a drop down and you can select the synth you want.

then when you click the blue fx tag on the track the new synth will show in slot one. and you can select the instrument you want.

one difference i think is that kontakt is not a GM synth - you can't just select it as a default synth and play GM patches. (at least i think i'm rigfht - i don't use kontakt but i thinks its like pforszando) you'll have to open a separate instance on each track and select the instrument you want.

try it and post again if you get stuck!