Those of us addicted to the Maggie sound have found ways to work through their perceived shortcomings. Two good REL subwoofers (I have 3 running presently) is a good step in the direction of addressing perceived lack of deep bass.
I also bought a pair of Maggie DWM panels - the same tech as the base panel in the 20.1s - to augment bass. It does do that but I often find I enjoy just as much without having them on.
The real upgrade came when I bypassed the external crossover box (which you cannot do with anything .7 or above) and actively biamped my Maggies. That was revelatory.
OP, you have many things you can do before you ditch your beloved 3.6rs! Forget about expensive replacements and roll up your sleeves!