The users manual for REW is a challenge. Read it a couple of times before setting out on this adventure.
It might be informative to read another, more compact take on the use of REW. This one at the MiniDSP site.
Link. It talks about using REW's ability to automatically create the filters.
OTOH, I have used REW to help dial in my PEQs for several years, and I like to do it manually, being somewhat of a control freak. Plus I like to use the fewest number of filters possible. It might need only one notch filter to dramatically improve a subwoofer's "one note" room resonance.
First and foremost, REW will provide important data on the speakers' frequency responses. That will be an eye opener. From there, you can decide how much (or little) correction you might want to apply. And finally it will help you splice the subs with the mains optimally.
Even if you do it manually (change the EQ filters from Auto to Manual), REW lets you apply filters to the measurement and see how it will be affected. It is a very accurate predictor of the end result. You can look at the measurements/results with different smoothing as that can help reveal how it will be heard. Some of those scary peaks/dips in the response are not as audible as they might appear with no smoothing, so applying 1/6th octave smoothing can make them more relevant.
Doing this manually a few times and listening to the results will really help train your ears about the nature of response errors that matter and how to address them with EQ.
The sound is quite loud so get some ear plugs.
Or turn down the volume. Unlike typical room EQs, REW can work fine at lower SPLs as long as the background noise is low, and as long as REW does not give you a level error message.
The 976 has shelf filters which are different than high and low pass filters (in fact they are just opposite). If you aren't familiar with these, there are some articles on the internet.
Easiest way to see what any of these filters does is to open REW's EQ page, select Model 976, open a manual EQ filter and play with the settings. You'll see it on the graph.