PBR materials vray CPU question

[till_botterweck]

Hello,
i am confused about rendering PBR materials.
Is it mandatory to convert PBR to Vray materials in Vray6 3dsMax 2024?
Do i have to use the 3dsMax Scene converter first ("Phsyical Material" to "vrayMTL")?
From my understanding the PBR workflow is used to avoid having to convert Materials between 3D hosts and renderers.

I do have a to render a Product that comes as FBX and is supposed to be fully textured.
If i load the Materials to the MatEditor after linking/importing the FBX they are all PBR materials and have all textures setup.
Assett tracking also shows no missing textures; also no warning about missing textures when i open the Scene.
However, the Materials are rendering not as expected (many glossy plastic parts and lots of metal parts in this product but).
I tried the V-ray Scene converter and checked "convert physical materials to vrayMTL" and the rendered image does look the same.
Also i opened the fbx files in autodesk "fbx review" and the materials seem to display fine in there (glossy parts are glossy; metal parts look metallic)

Any suggestions very appreciated, its a bit confusing.
thank you in advance!

[hermit.crab]

Usually, it is not mandatory to convert your setup to VRayMtls. Could you share (either attach it here or send) a simple scene so we can troubleshoot it? How big are the differences? Note that the FBX preview could be off to some extent and that's normal.