"The best way i can describe the problem is the highs sound like shouting instead of singing".
Blazen69 ... Is it possible you could mean the PEAKS (not the HIGHS) "sound like shouting instead of singing"
The PEAKS would be the loud passages ... the HIGHS would be the Upper Frequencies
I bet your high frequency response is probably alright or very acceptable even without any room treatments
I think your problem with the shout-y-ness occurs when there is a PEAK or DEMAND in the music for a brief second ... once this demand passes shout-y-ness stops and everything returns to normal and sounds fine.
If you had issuses with the HIGHs ... I sure you would be complaining about an edgy or fatiguing sound, all the time ... but your not
You problem is shout-y-ness and only momentary
If my description of the problems sounds correct to you and it's the PEAKs not HIGHs that sound shouty ... I pretty sure I know the problem and the fix