If your native soft synth sounds poor and flat... just add to the output the "SOFTCLIP S" effect from scope's FX extension, and if you're not satisfied add a second "SOFTCLIP S" in serial mode, and tweak both the levels.
I use this trick for my NI FM7, Reaktor and a lot of free VST stuff: all becomes more FAT and Funny!
FM7 becomes more (and really) close to my Yamaha DX7II's sound.
Is a good solution for guitars and voices tracks too...