I needed to do this exactly to hook my promedia sats to a new Logitech Z-2300 subwoofer/amp that only had RCA speaker outputs. What I did was cut the ends off one end of a set of RCA cables and separated/tinned the ground and positive wires inside and hooked them to the terminals on the promedia satellites. They sound GREAT with the Z-2300 subwoofer. The ground wire is the outside wrapping wire, the Positive wire is in the middle.
A rant--I'm really peeved at klipsch for their crappy amps in the Promedia 2.1 and Promedia ultra 5.1. There is no excuse for the failures on these amplifiers, and Klipsch not standing behind them. At least I could reuse my klipsch satellites with the new system.