well u have plenty power. thought u were slackin in power. still 4xl 18s sound good for that for burps but daily level 5 18s would handle that easy. that is in that 8 15 BP u mentioned.
the reason that 4 18s sux is people dont do the math...
while 4 18" giant cones moving is awesome... to this day and age coils are unable to handle larger loads than 2-3500 watts rms... it is better to have several high power coils to disapatte that energy...
I would like to see a vertical clamshell with a loading wall on the front and a port behind the drivers side. Eric Alexander did that a couple years back with 24 Crunch 12s and he was in the 60s on music.