ATC active vs. passive

@ei001h 

What speaker cables are you using and what power cord for your 595? Had that amp 2x and it’s pretty sensitive to power cords. Top end can can trimmed to your tastes pretty easily. 

On my SCM40 I am using Audience Front Row and a DPS 4.1 power cord. Seems to be excellent synergy between the moon 761 power amp and speakers. I have no issues with treble and think the top end is detailed and refined sounding.

I did notice a difference, for the better, when I used DH labs silver jumpers. I am running the jumpers between the teeter and woofer (using the stock plates for now to mid) and I do the AudioQuest recommended way of connecting the speaker cables across the binding posts. 

Lastly, how many hours are on your SCM40’s?

cheers

Speaker cables : 

1. analysis plus solo crystal oval 8 

2. nordost hemidal 2

power cord 

1. Analysis plus  Ultimate power oval 

2 analysis plus power oval 10 

stock jumpers 

scm40 has 500h

I used to have  Analysis Plus full loom (same speaker cables you have) and found it clouded the soundstage. Eventually moved to Purist audio and Nordost for power which was a step in right direction for opening up. Not a fan of AP for power cords on any component. Totally different system, but I think you have many options of tweaking the top end to your expectations. I have found the ATCs to be a very neutral reference. 

Had Heimdall 2 on my Harbeth shl5+XD and found the sound too warm, almost muffled sounding at times.  Audience Au24 sx was much better.

https://partsconnexion.com/speaker-bulk-cable/
For not much money, I believe you can improve your lot.  Also, dpac996 is correct with the Furutech DSP 4.1 recommendation.  Cheers

@ei001h I was looking at the other amps you used with your SCM40’s; The Mastersound starts clipping (1%) around 10 wpc. The Grandinote is rated at 37 wpc and starts clipping (1%) around 30 wpc. Neither amp produces close to double the power as impedance goes from 8 ohms to 4 ohms. The Luxman 595 (very familiar with this, as I used it for many months with Harbeth SHL5+XD) is rated at 30 wpc into 8. The 595 is the most powerful amp out of the three. However, given the Class A envelope and overall low eff of the SCM40’s I can imagine a sound that is not all that stretched out at the extremes. The SCM40s need a wide power bandwidth amp (minimum 75 wpc, better with more power) to show the listener what they are truly capable of. If you don’t change your amps but get the larger ATC’s ( even more power hungry) I am pretty sure you will not get that sparkle and air you are missing.
I am confident that amps such as Luxman L509X/Z, Ayre VX-5 Twenty, Moon 760/761, Boulder 866, Gryphon Diablo 120, etc., would bring you the added sparkle and improved dynamics that I think you are missing with the low power class A and tube amps.