Example, look like these?
Are the IC cable RCA plugs hard to push onto the RCA jacks on the ARC LS25?
Looking at the plugs they look like they would be.
Just a guess you are not pushing the plug(s) all the way onto the RCA jacks on LS25. Center pin of the plug is not making a good contact with the center contact of the jack. Try pushing harder to make sure the plug center pin is seating correctly into the jacks female hot signal contact.