I recommend using a box simulator software to model the box using your specific drivers.
I use WinISD for many years. It is free and works well. There are many other box simulators.
https://www.linearteam.org/You can combine drivers in one box to achieve SPL and impedance that you desire.
The Crown amp has DSP so you can EQ the subs to provide flat response in your room. This also means you can change the Q of the system so the box can be smaller than without electronic DSP, and sound the same as with a larger box. As long as the driver power rating can handle the boosted signal.
https://sound-au.com/linkwitz-transform.htmGenerally a sealed alignment is best for music because it has the best transient response and the least group delay, so it is lowest distortion. Passive Radiator and reflex ports are tricks to make lower louder bass without the expense of all active drivers. But all active powered drivers is always best for sound quality.
Your amp EQ will let you force it to play lower than it would in sealed box without DSP, just as low and loud as reflex ported speaker, but sound much better.
