Hi coilbook,
You could use the Material Selector, witch is a Composite material internally, and uses a standard Multi Material as input.
But it's getting a bit complicated, as you need to add an Octane geometry modifier, to assign the material IDs from the mesh..
And the actual material selection depends on both the internal geometry faces and material ID, so it's not fully reliable..
Top cube and plane use simple multi material on their 6 materials.
Bottom ones use the Mix material + Material selector
I'll try to improve this a bit, and remove the need for the extra mult texture..
Thanks
ref:
Material Selector tutorial and samples
viewtopic.php?f=27&t=80663