I hope what I'm about to say isn't out of place amongst all you techies, but I haven't got the first idea what you are all talking about....what is a soft synth when it's at home?.
I've played arranger keyboards live in all sorts of venues over the past 10 years and unless you're talking about rap or hip hop I've never had any trouble reproducing reasonable live cover versions of most everything that's been a hit over the last 50 years.
What are you trying to reproduce in terms of a musical sound?
Roger M