one thing people overlook when doing that is what input signal the amp can handle. No sense in getting an 8v line driver when your amp can only handle 4v. If you decide to go that route just make sure you're aware of this.

Back to the topic, the most important attributes of rca cable are shielding and capacitance and connectors. Heavy shielding protects audio signals from interference from outside sources. Capacitance can be important, particularly in long cable runs, because it contributes to rolloff of higher frequencies. Connectors are critical because if the cable isn't well joined to the connectors, or if the connectors don't make firm electrical contact with the jacks, it doesn't matter how good the cable is.

Stay away from cables with plugs like these


And get some with plugs that look more like this


Hope that helps