Yes, sounds like a very long phono cable. I would take a picture of the cable and send it to Cardas and ask for their comments. I never seen or heard of Hex5C with a grounding wire, but you never know.
Cardas Hexlink Golden Five : IC with RCA
I recently got these ( used) Cardas Hexlink Golden Five IC with RCA connectors ( 5 mt long ) . They have a loose wire ( about 9 inches Long with Lug type end connector ) joined at each RCA connector . It looks like for earthing or Ground connection. But I am not sure . Can anyone advise me as to what I should do with this loose wire ? Where do I connect it ? If I do not connect it to anywhere , and just leave it loose , will that be still OK ?