Hi,
Well, really when 'Use Segment Material' is enabled, RailClone doesn't create a multisub material.
Instead, it sends the single materials directly to the render engine. Although 3DSMax doesn't support multiple materials by object, most of render engines have not this limitation.
For you case, i see several options:
1.- Convert RailClone to standalone objects using
RailClone Tools->Instantiate. This generates separated Max objects, each one with its material.
2.- To improve performance while keeping RC objects, use
Display->Proxy Cache->Embedded. When enabled, RC object is locked and rebuilds much faster (it can be disabled at any time).
3.- Use a third-party script to generate a multisub material from multiple objects, and then assign this material to RC (disabling 'Use Segment Material').
Rappatools or
Assembly Tool could be used for this.