I have been thinking about replacing the ML with two smaller subs such as the REL T/7i’s or T/9i. I do like bass so I feel I need/want a sub. In my research I also keep reading that subs make the midrange sound better if you have the right setup.
Don’t replace, but do add the two. Even better, add three. The problem you’re having isn’t so much the sub being ML as that its just one sub. With only one you’re forced to move the damn thing around trying to find the one spot where the magic happens and the bass is extended and smooth. But the magic never happens. Never can. Because, physics. No matter where you put one sub it will always result in lumpy uneven tubby bass that never goes as deep as you want but thumps more than you want.
The answer is lots of subs. The more subs you use the lower each one can be, you be able to turn the ML down a lot, and this helps reduce boominess. Also with more subs you can set it to roll off lower, maybe even completely eliminating any output in the boominess range. Another thing that helps is they go different locations so create different modes in different places and at different frequencies. Finally you are not relying on one alone to extend really deep. These things all add together to result in much smoother, deeper and more articulate bass than you could ever get with just one sub, EQ/GIK regardless.