I bought some Owens Corning 703. Now what?

I somehow deleted a long post. I'll try again but keep it short.

6 x OC 703 panels will help but not all that noticeable. Buy a bunch more as they will not go to waste.

For the biggest impact look at taming bass frequencies which creates acoustic havoc in any domestic room. Make 2 stacks of 3 panels placed on either side of your system. Set these up lying horizontally at 45 degrees straddling the floor/wall corner. If you get more panels do the same in other corners. The more you have the easier it will be to see the result on REW.

The best advice I can give you is to become comfortable with REW, especially regarding the CSD (waterfall) plots. Once you begin to absorb the lower frequencies which are, because of combining either constructively or destructively, creating peaks and nulls. It is difficult to appreciate the harm done by these peaks and nulls or partial nulls. Consider that a null has nothing to contribute to the sound, it's music that's missing. Gone.

Bass can be well smoothed by using a DBA but will still need cognisance taken of the decay time. Using acoustic smoothing in the modal region in addition to the multi-sub approach will optimise what can be done. This double attack on the bass gives stunning results.

I see @ tomic601 is the only one who wisely mentioned RT60. This mysterious quantity is simply the time it takes for the sound to decay by 60dB which for the average domestic room is about 400ms. The target then is to have the full spectrum decay within 0.4 secs. REW's CSD plots provide this info.

Expect a correct RT60 to provide bass info previously missing or partially missing depending on the depth of null and more control and bass detail.
It appears poor @ shalommorgan did not go this route and required 5 iterations to get things sorted. Using REW or HolmImpulse (as used by Geddes), get the table off the net for RT60 for your size room and have fun.

The result of a correctly treated room is difficult to conceptualise but it is a bigger move to believable, rewarding and immersive sound than an expensive component upgrade. True story.

@lemonhaze
Thank you for taking the time to articulate the important things, in useful form. As the diagram on my system page will show (and which my measurements confirm) the corners are not that problematic.

( see: https://systems.audiogon.com/systems/9064 )

Given that, would you suggest 2 stacks of 3 panels somewhere else? Where the bass frequencies are the loudest? Or somewhere else?

I'm getting help with REW and learning these additional plots. I've been looking a lot at RT60 since tomic601 said that. I'll look at the things you suggest.

Posts on this site have convinced me that I'm done thinking about gear. (And I just put a system together.) So now I'm looking for a correctly treated room, or at least the path which leads there. Thanks again.

There is so much great info on the net regarding acoustics and seeing that it is the acoustics of your room that is going to be the final say on what you will hear that I once again encourage you to delve deeper into this fascinating aspect of optimising the speakers into your chosen room.

It's of course possible to get a professional company to supply and fit the treatment but without an understanding of 'what and why' you will find yourself needing to hire them again at great expense to analyse and fit out the next room you decide to use for system. Also appreciate the fact that you, armed with the knowledge and REW, can design a huge bass trap to sort out a specific problem. Acoustics companies are reluctant to design and provide custom service. They have standard designs which in knock-down form can be couriered easily and a few of them tend to oversell.

This brings up another point which is if you have REW sussed out you can measure any treatment fitted by the pro's and tell them to stop when RT60 is where you want it. A friend of mine had to remove a bunch of panels that rendered his room too dead.

http://arqen.com/bass-traps-101/placement-guide/#quarter-wavelength-rule
https://www.youtube.com/watch?v=LJ59AQU1FUY
https://www.youtube.com/watch?v=R4agj6oZIaI
https://www.youtube.com/watch?v=41liBn-QNW4&list=RD41liBn-QNW4&start_radio=1&t=375

You may find these links useful. The last one shows a super-chunk bass trap. It's a little sloppy but provides an idea.

@mitch2 
A/V Room Service EVPs are made with/of:
"The EVP core is a matrix of precisely compressed high-density molded glass fibers, which allows controlled air movement through the fibers." (from his web site specs)
They work well for isolating equipment.

Brief update. I did some critical listening with one interesting variation: (a) the entire box of panels against the front wall with the front face of it OPEN or (b) with the cardboard flaps closed. Very, very noticeable difference in what it did to the bass. When open and absorbing (and not even ideally), it sucked in enough energy to render the bass much crisper, located, defined. No muddiness even when the string bass in the jazz I was listening to went to the lowest notes; I could hear fretting and very distinct notes. Closed up again, and the muddiness came right back to the low bass notes.

FWIW, a noticeable difference. I didn’t focus on much except the bass region, so I have no idea if it was over-absorbing or disrupting upper balance. But it helped the bass a lot.