I don't understand why you would hate the sealed box if it sounds outstanding... sounds like your right where you want to be. A ported box will only get slightly louder if you build it just right.
Chances are that if you were to buy a pre-built ported box that it would not be specific to your subs and would sound worse but probably a little louder. I don't know anyone who wants their system to sound worse.. You're pretty much left to building your own box to the exact specs they require. The manual states the best ported enclosure for them. If you can build or find a box that match the exact specs you will gain a few dbs and it will sound just as good.
I've always found that more power tends to achieve the best results if your already liking what you hear. sealed enclosures allow you to pour on the power, well above the speakers rated specs.
Lots of Loud Loud Bass <- Old people say what a jackass, lol sorry im 27 and I loved extremely loud bass back in the day. Now I enjoy the sound of a loud tuned system without bloated muddy and distorted bass. Too much bass is easy to achieve, its the mids and highs that are difficult to get right. I'm guess I'm getting to old.
Toreador Red 05' FX4
4.0 4x4 A/Tran Ext.Cab Daily Driver. Nomads, BFG M/T's
Alpine 9857, JBL MS-8 DSP, US Acoustics 2x80w & 2x100w, Vifa 1" XT25 Dual Ring Radiator Tweeters 3k+ 24db slope, Dayton Audio 7" RS180-4 Mid-woofers 100Hz-3k 24db slope, 500w rms Kenwood Class-D Mono - JBL 10" GTO1014 Sealed. 100Hz- 12db slope