Not sure to understand the main issue, but if you talking about the way it looks in multipass and the beauty pass (main one)
You will spend hours trying to match your passes to the main one.
A few recomendations are:
-Render using Linear color Space.
-Use 16 Bits/channel or 32
– You are using Globall Illumination, add that to your Multipass too.
– Increase your anti aliasing to 2×2 4×4 or better, or try to render with the Physical render.
-tweak your settings with your compositor (after effects or Photoshop), like colors, blur, curves and so.
Hope that helps.
Good Luck
Imagination is the best tool…