I currently have (2) JL 10w0-4's in a sealed box behind the seat of a reg. cab truck. I have a JBL bp600.1 on them doing 600 watts rms combined to both subs (parallel), and it is beating the fug out of them. I have .75 cu. ft. in each half of the box for a total of 1.5 after divider and sub displacement. My question is: would roughly .5 cul ft. per sub be enough if I added a third? My thinking is that if a 1.33 ohm load draws no more power than a 2 ohm load as I have it now, then three subs would take the power better than two (roughly 200 rms watts each vs. 300). Subs are rated at 125 rms each. Would this poly fill stuff help with the smaller volume? BTW, JL recommends .75 each for sealed subs, but somewhere I had heard .5 to .9. What do you guys think?