balanced cables

I have an 80' run from primary system (18b as pre) to secondary (bel canto pre1). Using top of line rca cables I get a lot of hum-can't eliminate. I tried my mike cable on the right channel-hum dropped 15 db and fidelity seemed fine(WOW!). Why would I need to spend a lot of money on stereophile audio xlr's when the mike cables (lots cheaper) seem to work fine. Primary preamp is Soundstage with xlr outs, so I can do away with the 18b. Thanks for any help.
I've been making balanced cables with Mogami Neglex 2534 mike cable for many years and it's great. Most recording studios use miles of it, so chances are that your music has been through it before. Don
High quality mic cables are just as good as any other audio cable. I know a lot of people are going to say I'm wrong but that's the way it is. But just in case you don't believe me most good audio cables are balanced. All you have to do is replace the RCA's with high quality XLR's like Neutrik.