Some progress anyway.
I cleaned up from Sonar8 and SonarLE. I re-installed P5. No joy. I renamed the DimLE directory in 'Program Files/Cakewalk'. Re-installed the Dim_DXI from P5 which re-created the dir. Now the chains work. Something (perhaps the DimLE that installed with DSF packs, maybe SonarLE, who knows?) apparently corrupted it.
I also had to re-install my Rapture to get a DXI version in place. So, now the chains are loading correctly.
However, my DimLE VST is now missing a gui file and its directory appears to have been overwritten, though only the DXI should have been installed.
It appears that the 'regular' DimLE overwrites the P5 version used with chains even though P5 should just be using the obsolete DXI and the 'regular' version should just be a VST. What a mess.
I'll look into this a bit more tomorrow.