Both the 801 and the 802 will benefit immensely from subs. You are not just getting a speaker, you need to marry it to a room. The optimal location for imaging and so on is usually never where a sub bass driver oughta be. So, any speaker will benefit from subs (full range or not!).
That REL is not the brightest idea for your use case. Consider the ELAC Varro line, especially the DS1000 dual force balanced 10inch for your use case....and it is cheaper than the REL, how about that?
https://www.elac.com/series/varro/dual-reference/ds1000-10-dual-subwoofer/
Why?
Well, in your use case
a) Sub driver size is much more closely matched to the bass drivers on your speaker. If you don’t have servo control (from the likes of Rythmik), this is an important factor.
b) The Elac Varro will give you extension out the wazoo, dig into 14, 15hz, without blinking (something your Rel mentioned above can never do). You will perceive things in tracks that you would never hear otherwise, i.e. in a sub with weak sauce extension.
c) The Varro line comes with a very unique auto-calibration feature that is extremely beneficial for 2 channel purist systems without any PEQ or whatever else. It was pioneered by Andrew Jones when he was still at ELAC. At minimum, the calibration will match the sub’s response right at the driver to your listening position, even if a user knew diddly about how to integrate a sub. In other words, it will nullify the room’s confoundance with just a simple bit of positioning and running the cal. It will also give you several bands of manual PEQ, delays, etc/whatever else for more advanced users.