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I would have thought S8 already did auto-conversion of sample rates by File > Import if not also by drag 'n' drop Otherwise, you should consider an upgrade; all other methods will require extra steps.
 
EDIT: I just checked the 8.0 Ref Guide and confirmed for File > Import:
 
"If the sampling rate from the Wave file does not match the sampling rate in your project, then it will be converted to
the current project’s sampling rate and bit depth."

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Since you've already established that direct copy-paste isn't supported, I think your best alternative will be something like this:
 
- Drag clips from the source project to a system folder - they'll be exported with file names based on the track names at the source sample rate.
- Set Now time and track focus in target project, and File > Import > Audio from the system folder.
 
 
 
 
 
 
 
 

I do not know if the broadcast wave clip export in Platinum would save some time but it might.

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