The cables need to be 75 Ohm. Whether they are marked video, RCA, or digital, it doesn't matter. Just as long as they are 75Ohm. If they are not, you will have sync errors, or no sync. Also you shouldn't run S/pdif cable more than 10'(feet). Otherwise you will have sync errors, or no sync.
Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com