ESCDMA

To All, pls give me the reason why sub clipping, it is overpowering or what?, I have 2 subs rated power 400w nominal, model TS-W306C pioneer. It was hook up to my GM-X924 with 150w RSM X 2, my freind say it's good but for me I think it is under powering, Now I change my Amp MRD-M605 Alpine rated power 400w RMS - 4ohm @ 14.4V and 600w RMS-2ohm @ 14.4v. My HU is also pioneer DEH-8650 and the RCA out put level is 6.5V. Even when I put the gail level of my Amp to 2.5V the clipping is still there when my main volume is at 50%. there is many adjustment in the amp but when I put the gain into 7V and the Bass EQ is in the highist level, No clipping but it's useless my Amp I'm not happy because I can not hear the power of the Amp. Pls give me the advice what I should do, replace the sub? or what. Thank's in advance