The difference is not so subtle for me: better definition and a bit wider stereo image. This is one of the main differences between Nebula and all 'console' emulators out there: versatility. Once you start using these programs for panning as well as inputs, preamps, groups and mixbusses you start noticing that spending money on something else is quite pointless. The quality and results are quite beyond all current options in the market, in my opinion.
I'd strongly suggest you to try it for yourself. I use REAPER and this is quite easy to set up there because we have no different track types so I just split my stereo tracks in 2 tracks and add one instance on each, hard L/R.
i7 3770k :: Asus P8H77-V LE :: 16Gb DDR3 @1600MHz :: Geforce GT 520 :: OCZ-Vertex 128Gb :: WD Black Series 1Tb and Green Series 1Tb :: F*******e Liquid56 :: REAPER 64bit and StudioOne 64bit (both latest versions) :: Win 10 64bit
In Cubase or Nuendo is a real pain which is why I say it's impractical for me.....either you need to render all tracks requiring panning as stereo files or assign them to stereo groups...very quickly becomes a headache