Cannot melt CJ solder with 60w iron.Help

I was ready to upgrade female RCAs on CJ Premier Ten to WBT Nextgens but was unable to melt the factory solder with my trusted 60 watt soldering iron.It didn't even show me that a 100 watt iron will do the job.It was like trying to liquify a rock.How should i proceed?The input change will definetly bring some improvement to the sound but this is the first time i encountered this problem.Please,help.
I believe that is a brazed joint - not a soldered one. You will need some heavy duty equipment that can produce 850F at a minimum. I wouldn't bother changing them out but there is lots of info on the internet about brazing if you are still interested.