Maggie MMG versus Ls3/5a

MMGs are very good for microdynamics/transients but not for macrodynamics/"slam", ie dynamics you can feel as well as hear.

I would expect significant sound differences between Magnepan in general and Ls3/5a or any similar British monitor.

You might consider more high efficiency horn designs for that. Might not have to cost a lot or be too big if lowest octaves are not a concern, similar to mmg.

IMO, MMGs provide great value at $600/pr., but they do have limitations in dynamics and deep bass. Then again, I'm not familiar with any $600/pr speakers that don't have limitations. Certainly the LS35a shares those very same issues with the MMG. Presumably, the OP uses bass extenders in part to address those issues, so.....

I took a similar approach and use MMGs with subwoofers. Freed of heavy lifting below 80hz, they sound really, really good (to my ear, anyway) - better than any other speaker system that I've heard at the price point, and by a pretty wide margin (again IMO). There are a lot of good speakers at +/- $2k, but a pair of MMGs with a pair of good $1400 subs is that rare option that will also provide true deep bass. Dynamics are very good, tho ultimate SPLs remain limited. Timbre is excellent and octave to octave balance is satisfying, even if the high end may strike some as a touch dry. I find that imaging is also convincing, provided you like the way planar speakers image. (Not everyone does.)

OTOH, to make such a system sing you need to properly integrate the subs. I cross actively and the appropriate electronics will add to the total system cost. There are a lot of ways to skin a cat in this price range, but I do like the MMG+ sub+active electronics approach. Just one more data point for the OP to consider.

To different speakers its not VS its what you like!!

Are the dynamics of the planar vs a box speaker different from each other in quality? I don't mean 'slam'. I thought the MMG speakers could still exhibit good dynamics, but not visceral body 'slam', (because they radiate equally front and back).

Martykl, the Ls3/5a has pretty good dynamics and bass. The bass extenders are only necessary in a larger space like mine. But in contrast, I would like to experience strong attack, which doesn't happen with the Ls3/5a. I'm not so focused on deep bass, only just enough to convey some realism....PRAT, I suppose, is what I'm talking about.

Maggies/planars are top notch on transients I would say with most any amp and "attack" ie the leading edge of a transient in particular.

Some box speakers are as well, but many are not, and amplifier used is a bigger factor here as well I think.

"Monster" SS amps should also serve you quite well to help get those top notch results for "attack" in particular out of mmgs.