Maggies and rolled off treble

It depends on the power-amp & other electronics you are matching it with.
If you have top notch electronics, then I can assure you it is one of most musical speakers ever made.
Especially the midrange of the old Magnepan is au par with the immortal classic Quad ESL 57.
Poor electronics won't let the old magnepans sing !!!

That may be true of the older maggies but from my experience the new maggies are hot on the treble if anything.

the new maggies are hot on the treble if anything.

Indeed on the 3.3/3.5/3.6 series. Unless the system has a severely rolled off top end, a power resistor value of 1-2 ohms is a must on the tweeter attenuation terminal.

Do the older models also have such terminals? If so, is there a resistor there? And if so, try a lower value or none at all.

I have MG1.6, and a spectrum analyser to determine frequency response. The 1.6 does roll off the top 1/3 octave a few dB, which I can correct using an equalizer. Other than this top 1/3 octave the high end range is really flat, as per the Magneplanar specs. The owner's manual suggests that you may want to use the 1 ohm tweeter padding resistor (that they supply) to roll off the trebble. They say that a flat speaker may sound "hot" on the high end because recordings are often boosted on the high end to compensate for the rolled-off highs of many brands of speakers. With Maggies, the choice of tweeter padding resistor is left up to the user. Nice.

I would expect the Maggies which use the ribbon tweeter to be flat to, and above 20KHz as per the Magneplanar specs. However, they probably also need the resistor to sound flat with many commercial recordings.