One quick suggestion for you is to go into Voice Edit and experiment with increasing the Touch Sensitivity settings. Of course if you increase it too much you lose dynamic range. But I find increasing this helps bring out the details of the sample more, especially if you are going for that “bigger” sound like the demos that cuts through the mix, which is what I think you want. Also increasing filter resonance and EQ brightens the voice as well, and of course effects. Leigh Wilbraham’s YT videos explore voice editing on Genos, which is the same on SX.
When I had my MODX I saw this same complaint from users, especially the pianos and other sounds that people felt didn’t sound like the demos. These were some of the solutions on MODX and they also work for SX.