How to tame a bright system?

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.

This was as close to Unanimous advice as I have ever seen on Audiogon, a clear majority identified the culprit right away. Yet OP defends the sound of his overly bright B&W speakers, which he “tested”?  Then at home he heard what those speakers really sound like, but rejects the evidence of his own ears.    and the op’s system resource allocation is absurd, as several people pointed out.

It’s an old story.  Pearls before swine. 
 

Sorry OP - this seems very, very unbalanced: a high dollar, highly resolving upstream, paired with $900 metal dome tweeter 2-way bookshelf speakers. The Fire XLR alone lists at $3,500 / 1m. I think a lot of folks would’ve predicted the issues you’re having.

Obviously, you’ve got a lot advice to fix that imbalance. What you have, would be a great upstream for a lot of nice speakers.

On to cables - as others have also mentioned, the Fire is not exactly a relaxed sounding cable. It’s a cable I love, but it’s a little bit more aggressive than even other silver cables in the AQ line. I find my 1st gen Wild Blue Yonders are a little warmer and more relaxed than Fire. The Fire’s predecessor Sky (also 1st gen in my case) was also certainly warmer. The Wind is not the right move - it’s overall similar in tonality to Fire, but lacks the latter’s bass impact and body. And the WEL Signature sounds very much like an extension of the Fire. In fact the Fire sounds like like a WEL Junior. I’ve had both RCA and XLR pairs of all these cables. I’m not sure if later versions of Wild and Sky carry forward the 1st versions’ warmth, but those and the very limited "Horizon" model are worth looking at when they come up used. Quite honestly the v1 Wilds are probably my favorite. The copper cables (I had Colorado RCA and XLR) are a LOT warmer, at the sacrifice of some resolution. 

@millercarbon

Really whats wrong with measuring even when it cost you Nothing only than a measuring Mic for less than a 100 bucks. If you don’t like the result heck bypass the sound an be happy. Let people decide them self.

One of the solution the latest room correction can bring you.

• Corrects deficiencies of room acoustics (multipoint compensation).
• Corrects acoustic imperfections of speakers.
• Avoids the pre-echo (pre-ringing) problem of conventional convolver-based room correction systems. The absence of pre-echo ensures the neutrality of the sound.
• Works in rooms, halls and outdoor venues of any size.
• Works with zero latency. Perfect for live performances and studio monitoring. Doesn't delay the audio track when playing video.

• Performs frequency response correction, phase response correction and time domain correction.
• Quells resonance peaks of frequency response while leaving the deep notches. Avoids the overcompensation which happens in conventional linearizing room correction systems.
• Manually adjustable level of compensation allows one to reach the maximum transparency of the sound.