I never understood why people tell room acoustics is expensive! How much is a pack of rockwool?Well, somewhere in between the extreme positions of: "it's too hard--get out your checkbook"...and "it's too hard and too expensive--you can't really do much but these [mostly ineffective] treatments" is a vast domain of DIY acoustic treatments.
It's about 10 bucks per m², up to 30 when you take nicer material and more thickness. The rest is optics - you can spend as much as you like for that.
The earlier you plan acoustics during building/setting up your room the cheaper it is.
Could you set a 60dB range, maybe 90-30dBSpl?and finally, the RT Decay plot:
Your reverb curves are not bad. You have a problem around 300Hz and a rise in the 2-5kHz area - the most sensitive area of the ear. And of course the high frequency fall off. Low frequencies are pretty good - american light walls house?
So the first goal would be to lower the over all reverb - BROADBAND! So only use deeper absorption - don't use any if that's not possible.
There are so many places where you could add absorption! Corner wedges are efficient for what you need (lower reverb >80Hz) and you have a lot of possibilities around your ceiling to install something there! Use the area behind your speakers and esp the corner of your right speaker. Put something to the shelves behind your listening postion!