actually the kappa and kappa pro wont do very well below 200hz
and in a sealed box would barely handle 50watts below 200hz.
Even though the thermal rating is high around 450watts that is because of the large voice coils and will only achieve anywhere close to that power handling with a high pass filter at 100 to 200hz as a pa midbass
the delta pro 15a would be a better canidate
and a few others that would survive better in a sealed box.
also adding damping material to that speaker chamber will improve the mid range clarity. just line the walls with blanket batting