Wool Blankets as Room treatment

Only in the highs and at what frequency I am not sure. If you have slap eco go for it. But honestly most treatments should be broad band at least 6’ think. You can heavily treat a room without it being too dead. The key is to treat the full spectrum and not just nuke the highs. Under 60hz is very hard to treat and that is where subs and room correction come in IMO. 

@james633  Yeah not going after anything really sophisticated.  Room is just a big echo chamber now and just trying to achieve subtle improvements on bare painted drywall and not make is look like a recording studio.  

I like the idea of the GIK diffuser panels alongside the wool blanket.   Proly do the wall behind the rig for less than $1K

Start with bass traps to get the low end under control first. This should be the first step in treating a room. Measure the room as is and then as you add treatments so you aren’t just guessing. You really can never have too much bass trapping. Go as big as you can everywhere you can.

Wool blankets should work quite well.  One of the best rooms I've heard was one where the cement block walls were only covered in spots with decorative wall hangings and tapestries--no obvious and ugly room treatments were applied.  These minimalist treatments are akin to the wool blankets mentioned.

Among the worst rooms I heard--dry, sterile, lacking in life and unnaturally lacking in reverberation where custom-designed rooms where acoustic engineers/architects designed the rooms.  Maybe these rooms would work for sound engineers, but for home listeners I thought they were not good sounding.

I think that a lot of people who are serious about their systems end up over treating their rooms.  I would start small, like you are doing--treating the walls minimally with wall hangings.  It helps to have a carpet on the floor, or at least an area rug so that early floor-bounce reflections are somewhat attenuated.  Book cases, potted plants and other "normal" room objects that are placed to also break up reflections to make them more random would help too.  After that, you might consider corner bass traps--at least these can be not as ugly as other treatments (but, the bigger the trap in diameter, the better).  Another great room I heard was a very large space with modest amount of treatment (ASC corner and side wall traps).  The owner originally put in an extremely large number of such traps, but his dealer, when setting up the custom-made speakers, pulled out more than 60 of such traps.

My friend has a giant American Flag. I suggested he put 1/2" thick textured carpet pad behind it.

example, search Bed Bath and Beyond, many exist

Mohawk Home Felt Rug Pad 1/2" Inch Thick Plush Comfort Cushion - Grey - 5' x 7'