How to tame a bright system?

snarfie23, I’m sure you cut and pasted that. But in case you actually wrote it, when (if) you wake up from OD'd on the Cool-Aid, stop and think about what you "said"-

allows one to reach the maximum transparency of the sound.

Transparent means clear, you can see through it, as if nothing is there. But everything you talked about is altering what is there. It is manipulated. Far from optically clear transparent glass you want an image distorted with with lenses to look the way you think it should look. By definition literally the exact opposite of transparent.

All the rest is equally double-talk. That’s why.

Crickets.

Room EQ is a horrible answer. Always ruins detail as you have noticed. Another unavoidable problem with EQ it is impossible to alter frequency response without also altering timing and timbre. It is just an awful "solution" but it hangs around because it does make for nice charts, and some audiophiles are way more in love with their charts than their music.

Everyone knows your problem is your speakers. But you insist on not doing the one thing that will make the most difference. Instead you are determined to focus on cables. Even though you know you already have an excellent cable that makes everything better. Synergistic Research will get you the excellent bass and dynamics you like. There are a lot of used ones out there at great prices, and Ted has been making them so consistent for so long you can rely on that consistency and shop by price. Don't know if that will solve your speaker problem but kind of painted into a corner here on options.

Not the wire. Change the speakers. First find some with at least 92dB sensitivity that have the warm sound you are looking for. 92dB because this will give you a lot more amplifier choices, especially in your price range, that will also have the warm sound you want. Then you will find the Fire sound just fine.

Finally, put everything on Nobsound springs. Real nice improvement and with the added bonus they will allow you to further tune and refine to get just the balance you want. Nothing else out there even close, certainly not for the money.