Well the first thing is to get a known good cable to make sure all your interconnections are noise free.
Then test each signal path one at a time with only those known good cables and test each piece of equipment with those known good cables. Then you'll find the culprit.
A continuity ohm test of each conductor and pin of each cable is of course essential and as you've found out should always be done before ever connecting it to see if it works.
Yes you could have damaged the input or output circuitry of your equipment with mis-wired cables....!!!
Don't forget to check all pins in the connector and make sure you only get continuity on the correct pin.
Sometimes a strand of wire or solder blob can short across multiple pins and you may not see it but it will show up when you test them.
Check the Rane Notes for the proper terminations. This is a valuable sheet to have in front of you when doing your own cables or trying to figure out how to balance or unbalance a particular transmission line.
Sound System Interconnection