How to tame a bright system?

Don’t try any new Gear make use of room correction software like mathaudio room eq for free with foobar2000. Atleast do a measurments apply room eq an listen to the result with an without room eq it could be that you have horrible room acoustics. You could be in for a shock. There is no hardware that can compensate that.

Hi all, Thank you SO MUCH for your reply/comments. As expected, most of the comments are on the speakers.... 😂

Here is the story of 606s2. I went into a local store and tried almost all speakers within 3k including Dynaudos/KEF/Sonus Faber/B&W, and ended up with the 606s2. Among all speakers, 606s gave me everything I wanted, the subtle dynamic, sparkles in instrument music and deep bass.  I am afraid I can't agree on the negative comments on the "12k DAC+ 0.6k speakers is a poor combination". Cost does not mean everything. 606s are very revealing and a good DAC can make them shine. (but now just a bit dazzling 😂).

Why it is not working so well these days? I think I have lost the balance between "revealing" and "forgiving". I used to have a pair of KEF R3s. I love them but I cannot feel the emotion in the music when listening to KEF, meaning that they are forgiving and relaxed. Nothing will come out from the speakers to attack me but at the cost of emotion. Thereafter I "upgraded" to 606s2s and got everything I wanted. It went on well for quite a few months until recently I stayed more at home (COVID working from home) and started to feel the attack/harsh from some specific music (only ~ 5%) while most of the time, I am very very happy with the 606s. 

Here is a  youtube link to a piece of fantastic music (cello&Piano). I can enjoy the music till 2:30 . There is a harsh at 2:39 - 2:42 (an attack to my brain/ears). and a lot of harsh afterward. I am not sure if I should call it bright or harsh or edge. please help to correct me if I described it in the wrong way. Or maybe it is just the poor record. Such kinds of things are also heard from some other records mainly at the high-frequency part of cello/piano. 

I have tried several changes from home. Cables tried:

Audioquest Mackenzie (XLR)

Chord company clear way (RCA)

QED reference (silver speaker cable)

Audioquest XTRM split (copper speaker cable). 

Audioquest Rocket 44 (copper bi-wire speaker cable)

and some other cheap DIY cables.

Among all of them, XTRM split cables did magic work that reduced the harshness a bit. The cable seems to push all music into the wall and the harsh cannot easily reach me. Therefore, the "harsh" is not as obvious as before. Unfortunately, all others did not improve the situation. 

So this is the story. As I just started two years ago in Hifi, I believe many mistakes wrong conclusion are made in my post. I apologize for that. 

The cable approach seems doable but not a kind of day/night change. 

Speaker change could be a solution. Maybe something a bit more relaxed and forgiving. I am looking into Dynaudio Evoke 20 or maybe I just pick up a pair of R3s again. I do not consider any other speakers as I don't have them in the local store and 2k is the current wife-friendly budget. It is not wise to pay without listening first of course. I will visit the store on Saturday.  

All in all, thank you all for helping me out. I did not expect so many replies. Your kindness is more hifi than anything.  😜

Did you try the toe in/out suggestion?   Easy to try and nothing to lose. 

Yes, I tried toe in/out. Toe-in works a bit but not as much as the xtrm cable. Yet, the cable is not day/night. Thanks a lot for the suggestion. I can enjoy more than a few days ago. ;-)

I give you a example of my room accoustics.

The Grey line is the measured frequency response. Do you really think you could compensate (sometimes in the higher frequencies a 14db difference) that with any cables, dac, speakers etc etc forget it it is an endless quest that you go into. My or other speakers sounded extremely bright by using the white target curve my sound became completely balanced. If you have a room without any room modes thats another situation but in 90% of the rooms that is not the case. Measuring is knowing.