Speakers sound too bright.

@rwalsh07 Try one or more Akiko Audio tuning sticks on your Lumin, DAC, and/or preamp. In my system they definitely tame the higher frequencies.

The sound of speakers varies greatly during the course of break in. I try not listen to them during break in because inevitably they will sound awful at some point. I then think I have terrible speakers, when after they are broken in, they sound great. Try not to pass judgment too early.

I have played with ML speakers for decades and a few things to keep in mind are: 1) They are line sources that radiate in both directions and 2) they are a capacitive load not a resistive load.  

Others have mentioned room treatment.  Because they are line sources, floor, ceiling and side walls are not a big problem, but the back wall needs to be treated.  I think only having 1 ft behind the speakers is a big part of your issue.  Mine are 6ft from the wall and I have a combination of absorption and diffusion to tame the back wall reflection.  GIK was helpful in developing room treatments. I’d reach out to them.

The other thing that I have found is that most solid state amps are designed to drive resistive loads.  I have tried many high end amps, but always found the best results with a high power tube amp and a solid state pre.  A few years back I demo’d and then eventually purchased a SANDERS amp to drive the speakers.  It is specifically designed to drive ESL capacitive loads.  I then paired it with a tube pre.  

Speakers are only one part of a good system.  The room and amplification also need to matched to the job.  They are tricky speakers to drive and to set up but they are sublime once you do.  I also have large woofer towers to provide the bottom end.  

I spent a year with a pair of Martin Logan Motion 40's... the model below the 60's. I purchased them used so they were fully broken-in. Bright is not a word I would use to describe them. Sweet and airy is how I would describe the Folded Motion Tweeter. I sold them and still regret letting them go.

In my opinion they need more time. The manual with my 40's said to break-in @ 92dB for many hours if not days... I forget exactly the time specified. Personally I would not play them that loud but a longer break-in could be the key. As someone else mentioned, play them constantly at normal levels for a week or two or three. Or until the return window is near. Many days of playing time also made a huge difference in a pair of speakers I got with aluminum dome tweeters. And check for any issues upstream.

So you are getting a lot of advice that your speakers shouldn't be too bright.  I have a couple of thought.

1.  I have seen silver or silver plated speaker cables make the sound bright.

2.  You should confirm all the bass drivers are working.  play music with bass in it and gently touch each cone to confirm is it vibrating/moving on the bass note.

Jerry