sorry quick post before work very blonde if your using the XT4000D -i would recommend that you use either the 2pcs RE SEX rated at 600rms -10,12,15.same rating (comes both 2 and 4ohms now was strictly 4ohms before) OR 1pc RE SXX rated at 1000rms -10,12,15,same rating (comes both 2 and 4ohms) OR 4pc...