The jump from D200 to D400

[Womaz]

No offense but you may be making the classic mistake: trying to solve acoustic issues by buying better equipment, cables and tweaks. Sure you may seem to alleviate the issue at first but soon as one gets used to the changed sound the issues, that of course were never gone, "return".

You could try to find a friend or someone else in your neighbourhood who can make some measurements of your room or invest in a measurement microphone yourself and use a (free) program like REW. Remembering your description of your room a RT60 measurement is likely to show way too high reverberation times.

I am thinking the upgrade as an upgrade , not just to calm the brightness ....but if it did this it would be a bonus.
I am guessing you think room treatment should be given a priority? I think it's a good point but again I would not know where to start with this. All being considered though