For OP, if you can measure your room with XTZ RA pro II, you can order special tuned Scopus Traps. This way (measured), you can start off buying only several Scopus to start off ridding the modes. Measuring helps you and help Gik with two things.
1) Determine at what frequency or frequencies you'll have the peaks.
2) The actual level in db the modes are.
If you do not measure, you'll have to guess and might end up absorbing less specific which in turn, will not help you ridding the actual mode at that degree you'll need.
When measured and you know the actual level in db of the mode(s). You can tell that to Gik and they will be able to tell you how many panels you'll need. Also, custom make them to absorb (better/more) at this or these frequencies.
When that is done and installed, you can easily determine if you feel more panels are needed. Maybe not!
Ceiling usually is a problem. Concrete walls and ceiling can give a harder reflection. Some usually blame cables for being bright, this can be due to the ceiling, walls. Glass (windows) are even worse.
http://www.gikacoustics.com/gik_scopus_tuned_traps.html
I use 242 in the ceiling, but if i had bought now i had bought GridFusors. Placement in ceiling you can spot doing like this. Sit in your listening position, have a friend walking at each side between speakers and where you sit. When you see left speaker at left side that is first reflection, when you'll see right speaker at left side it is second reflection. Ofcourse, you can do same at right side of listening position. In line between these sides, the ceiling reflections are located. Now you can determine where to put ceiling panels aswell as side reflection panels. For example, in my room the ceiling reflection has a huge impact.
http://www.gikacoustics.com/gik_gridfusor_acoustic_diffusors.html
Bass boom:
For instance, i have a big mode at 43Hz (around 19db!).
So for me it had been wise to try Scopus and ask Gik to specially tune a kit of absorbers as close as possible to absorb at 43Hz. This i had never known if i couldn't measure my room. I can measure in corners and listening position where modes actually develops and at what specific frequencies. I can also see where in the range i have big dips (opposite to modes/peaks).