I've lusted after those M&K subs beam!
I've run subs two or three times. I think the big issue and why they're generally unloved is they can be hard to integrate. Fortunately I don't have a golden ear
My favorites (and the only higher end subs I've ever owned) were twin HSU original tubes doing low duty for tweeter modded DQ-10s. It was early on, I can't remember what I was driving everything with but my amps were probably low end. The room had a horrendous hump around... 70 hz? so I used Marchand active xovers with a notch filter at the hump hz. Worked well.
My young nephew was over, I had the stereo on very low in the background and he suddenly looked a little panicked and said 'was that thunder??' I turned off the stereo.
I think subs have a place in many systems. Even my last AR-9s could've used them occasionally methinks.
Pete