I have a DD 1010 hooked up to a Hifonics Zeus zxi6006. The Zues puts out 600rms bridged@4 and the DD is a 4 ohm SVC sub. When I hook it up the only way I can even hear it is if I crank the gain all the way up, and when I do that if I take the volume up too high the sub will stop playing but the amp will still be turned on. I tried another amplifier with the same results. Could this be from a bad ground maybe? Or what do I check? I tested the power coming to the amplifier and it is a solid 14 volts.