Most Magnepan-subwoofer setups suffer from what I call 'timbre mismatch', regardless of the crossover and level settings. And that is made worse by subwoofers that are home theater oriented, tuned for output not musicality. Certainly crossovers with a high-pass and lowpass are preferable, boosting power handling and panel output capabilities. However, my headbanger, tweeter melting days are far behind me, so lack of a high-pass function isn't a deal-breaker for me.
Stick with the hifi version of the subwoofer offerings, and a smaller driver (8") and your timbre match issues will be minimized. REL and SVS, as well as KEF all have great offerings that meet those requirements.
Coincidentally, my experience with both Magnepan and powered subwoofers goes back almost 50 years, both as an audio engineer and as an audiophile.