@T-Rex I got what you are saying now. As you have already realized with this, is that RMS is a value that has to do with what a driver can handle, which is independent from the box. In other words, the amount of power a subwoofer can handle in burst or rms is dependant on the box you put it in and even the frequency at which you are playing. I always design a subwoofer around the RMS number, since we know that we can safely play that continuously without damaging the driver (assuming the box/frequency etc). What you will find out when you start playing movies and music is that some dynamics will cause your driver to have excursion issues. THis really isn’t a problem as you will just put a limiter on your amplifier/dsp. THis will limit the amount of dynamic power in order to protect your subwoofers. One of the first scenes I test when setting the limiter is Live Die Repeat: Edge of Tomorrow. Those low notes hit hard and low, which help me set both my highpass and limiter. If you ever find a scene in a movie that does cause your sub to make weird noises, you just set your limiter again until your psub plays nicely.
Let me know if this does not make sense.
