Room is way too bright.

I feel your pain! My listening room has 2 4x10 floor to ceiling windows, hardwood floors, and a stone wall at one end. It was bright. 1st reflection is the stone wall on one side, then an open doorway on the other side. 

1. rugs, blankets over furniture. 

2. window treatments, fabric blinds works well, but you get no light (also affects plants) added blackout curtains (they are super heavy, made to absorb sound) also added shear coverings over the entire window. 

3. Fabric wall hangings. Have a few canvas pictures up, packed the backs with rock wool. There are 2 just behind each speaker. Along the long walls to my listening position. 

4. big plants. Have huge fern, a palm, other plants, they really do make a difference, and warm up the room. 

5. Weirdly, my record collection along the wall, helped calm the room down. 

6. Added L-Pads to my tweeters. Not sure this is really a thing, as they are replacement tweeters that are +6db louder, kind of needed to be done. 

I'm very interested in the ZW-damping disk. What are they made from? Are they just Sorbothane disk? Windows absorb resonate and reflect so much sound! 

Elimination of reflections of hard side windows has been discussed. Don't mess with the content or origin, simply eliminate the problem temporarily when listening, that's the flexibility of Acoustic Fabric Vertical Blinds. Keep all that daylight, a few live plants, a living space, not a dungeon.

Toe-In combined with Tilt, directing the tweeter's output in and up to your seated ear height, will give preference to direct, essentially equal volume of primary drivers, minimizing reflections from floor, ceiling, and side walls.

Ability to adjust frequency balance at listening position to your preference is important. CD with test tones to document pre and post adjustments, 

Amazing Bytes, CD with 29 1/3 octave test tracks

and SPL mic on tripod

SPL Meter, with bottom hole for tripod mount

are needed, then use your ears, a helpful friend is always good.

Open Space behind you increases the time delay of eventual reflections. Diverse mix of angles reduces similarity of reflections to initial direct sounds.

Adjustable Toe-In for Imaging, for Single Centered or Two Off-Center Listeners

Toe-In Alternates, Stereo and Video

Having a picture of your space may help us determine solutions.  The ceiling panel, also known as a cloud, is probably your best bet without covering your windows with absorption.  Handling that ceiling bounce will at least mitigate that reflection angle and may make the space much better.  I also agree with speaker placement and toe in are critical and by moving your speakers away from the windows, you can reduce the amount of acoustic energy hitting the walls.  DSP and cables are the absolute last thing I would do.  Building panels is not hard, or you can reach out to a company like gik acoustics and order paneling from them. 

@8th-note

I really like your approach!

As noted by others, reflections come from the walls and also the ceiling and floor.

If you want to minimise the accoustic mess created by different length reflection paths, use speakers with a minimal number of crossovers and separated drivers.  Think point-source, or an approximation of it.

That way the reflections are at least coherent, making it much easier for your ear/brain to hear through to the music.

As Magnepans essentially don’t radiate to the sides, I’ve found them to be much more forgiving of rooms with glass on the sidewalls.

I can open my blinds all the way and the sound is still good, just a bit “lighter” in tonality.