Metralla is correct. RCA (single eneded) cables are fine for relatively short runs. In order to take full advantage of "balanced" technology, your preamp and amp must be "differentialy balanced". Many amps and preamps out there have XLR inputs or outputs, but aren't differentialy balanced. Another advantage of XLR cables is if you have very heavy cables. XLRs lock tightley in place. Heavy RCAs can bend the center pin over time.
