System upgrade advice

Yes! The room. I am not familiar with the Proceed pre, however feel that the Rotel/Paradigm might be a too bright match. Possibly a warmer sounding amp might be in order as well.
Voice the room 1st.

I do agree with much of ZD posts, however I can’t help but believe that regardless of what you do with the rest of your system some dampening of the room via use of carpet and pad, curtains, and some acoustic panels at primary reflection points won’t improve the treble. A bare room is simply to alive IMO. You might look into ATS acoustics of Piper City, Illinois. They sell factory made acoustic panels and DIY supplies. There web site is good.

Where is the 8’ opening relative to the speakers, listening chair, and window?

Vjb, I think that Zd provided a very good response to my latest post. I also agree that it is likely the Paradigms are not to your liking, as they are bright with an 'aggressive’ tweeter. I owned the Studio 20s however had them mated to a Vincent 226 hybrid amp (tube linestage) which I felt leaned more toward the musical than analytical side. Not as bright IMO as Rotel amps I’ve heard.

While in the process of treating your room, you might also take your amp to dealers that have speakers of interest. You can hear the speakers as they sound driven by your amp, and also likely have a chance to compare them with another amp of different character. There are allot of very fine speakers at or below your stated budget for the 804s.

Good luck in your quest. Please keep us posted as to your progress.