The first thing you should do is invert phase at your Rowland amp or speakers by reversing the + and - speaker leads to both channels. That will get your main speakers in correct polarity unless your preamplifier also inverts.
Once you do that, you won't have to invert the subwoofer's polarity, except that this would only be correct if your sub is located in the same horizontal plane as your main speakers... that's why they give you the Phase control.
So assuming your sub is somewhere else in the room, you would then adjust the phase control for maximum bass output while playing bass-heavy music. After that you would dial in the sub's volume level vs. the crossover frequency.
All this will take some time and experimenting if you are not familiar with the process. But once you nail the settings, the results will be well worth it.
MJ Acoustics makes subs where all the above parameters can be adjusted from the listening seat via remote control as you listen. They also offer 4 or 5 different programmable curves.
You can do the same with the Paradigm, but you'll need to go to the sub to make the adjustments and then sit back down at the listening seat to judge the results.