Go active. Passive subs sucks power from our HU during high musical passage. Notice the flickering lights in your HU during bass filled music. A 50watts to 70 watts amp connected to your subs will do. Signal to this line is taken from your low level RCA jacks from your HU. Use your existing speakers for mid to high frequencies. This would be a modest setup, unless you want to go into crossovers and bi-amping.