There’s a lot that goes into making hardware sound the way it does. There’s the audio generated by the instrument itself. There’s also the signal path that it takes after leaving the instrument: cables, a mixer, possible outboard effects units, and an audio interface. All of these stages additionally color the sound. A VST synth, however, stands on its own, so the comparison is not necessarily valid. If you want the sound of hardware in the box, that is, in a DAW, start with the best-sounding VST synth you can (like Diva or Serum, above) and then add color with effects plugins that emulate the sound of top mixing desks and outboard gear.