Speakers sound too bright.

My experience with ML is they are not inherently bright.  The AMT tweeter dispersion pattern is not sensitive to floor/ceiling reinforcement and you said you experimented with toe-in.  Therefore, I would let the speakers burn in 300 hours before you critically analyze them.  That said, are the metal jumpers the “clips” supplied by ML which are simply a piece of copper, not a shielded wire?  When I had Apogee speakers, they came with similar copper jumper clips manufactured to the dimensions to slip between the terminals.  They had no shielding. The result was a grainy, harsh sound.  My recommendation is to use speaker cable, equivalent to or better than your current speaker cable as jumpers, or better, bi-wire the speakers. Both options improved the SQ of my Apogees, the bi-wire option significantly.  Bear metal jumpers can be a point source for EMI, including RFI, to enter your system which produces a glare like distortion.  I recommend trying this to see if it improves SQ.  Also, the AMT tweeter design has a wide dispersion pattern so I also recommend experimenting with side wall room treatment.  Good luck. 

Clarification:  the AMT design has a wide horizontal dispersion pattern, narrow vertical dispersion pattern. Therefore, no ceiling/floor reinforcement, but possibly side wall reinforcement.  

Besides brightness/harshness, what else do they clearly do wrong ? New not burnt-in equipment and cables can do many funny things at the same time. I can't know if this is the case. Find a few very high quality recordings and see what they do with them. Don't even listen to them for longer than a minute at a time before you get at least 50 hours of play. I suggest starting with low volume and then gradually increase it to moderate while accumulating hours. Don't push it.

I would think it would be premature to return them unless they just sound like a complete junk. This pair might actually be defective. So yeah, I would give it a try.

Any new speaker will require 100-200 hours of break in.  If you replace them have you thought of used speakers or store demos that have some hours on them.  
It’s painful for me breaking in new stuff which includes cables because I’m so impatient.

Brightness (lack of) is not usually what improves with speaker break in. What you normally hear in brand new speakers is a "tightness", the speakers don’t swing and let go of the notes. And the bass can seem somewhat lacking, the bass and midbass fill in when the driver suspension loosens up.

That said, a speaker can sound top heavy if the bass isn’t balanced with everything else. A tweeter will sound more prominent in a bass shy speaker. That could be what you are hearing and that just might change with more hours.

How long can you keep the speakers and still exercise the return option? If you have time, put a track on repeat while you are at work and let ’em rip for a few days. If they haven’t come around after ~200 hours, send ’em back.