I HAVE A KENWOOD KAC8152D MONO AMP (1100W MAX)(BASS REMOTE) WITH 2 12IN MTX RT1204 SUBS AND A SONY XPLOD DECK 52X4 AND IT SOUNDS LIKE THRASH NO RUMBLING BASS, BUT MY BROTHER HAS A KENWOOD KAC7202 (920 WATTS MAX) WITH 2 12IN PIONEERS AND A JVC DECK AND IT POUNDS WE BOTH HAVE THE SAME CAR 1999 CHEVY LUMINA LTZ MODEL, WHAT KIND OF WIRING SHOULD I USE A SERIES OR PARALLEL TO GET THE MAX POWER FROM THE AMP
Other than wiring - set your LPF to something around 80hz, maybe a little less. Sony tends to use 2v pre outs on their lower priced units (<200),>200) so set the sensitivity accordingly.
If you've done that, or it doesn't help it may just be the woofers. RT's aren't exactly high quality.