Technical Question - need input

[04GT]

hey guys. need help on making this louder. (gotta beat my buddy) logistically, mine should be louder.

im running a JVC KD 430r headunit puts 2.5v out the RCA's

0ga wire, from alternator to BOTH batteries, 0ga grounds, all grounded seperate.

i have 3 AudioPipe BD 12's running at .4ohms with box rise that brings it up to .90

i have an Audiopipe HFX 2500 RMS amp

box thts 5.5 Cubes, (with port displacement) tuned at 38.5 Hz.

not as loud as it should be.

what can i do? RCA signal booster?? get it at 6v?
any input is appreciated, as long as its not smarta$$.

thanks!

[I800C0LLECT]

Beat your buddy? What is his setup? What's the magic number? There's a few guys on here that are ALL about SPL. Hopefully they come out of hiding. I'd tell you to horn load

[04GT]

he has one american bass HD15.. and a hifonics amp..