I suspect your problem has to do with the efficiency of the w7. Look at the graphs I posted, the w7 was getting 1000w vs 500w for the others. 3 db higher means twice as loud. I don't have the program here now but I bet that with a true IB sub you could reach the same output on less than 1/3 the power.
Mobridge DA2 > JBL MS-8 > JL Audio HD600/4 > (3) Hybrid Audio L3SE & (2) Rainbow Cal25; JL Audio HD900/5 > (2) Morel HCW-10 & (1) AE SBP15