Advice about Tekton: replace ATC SCM20 SL with Tekton Electron?

I see the frequency range on the ATC doesn't go that low. Are you using a subwoofer?

Not trying to direct you away from the Electron, but have you looked into the Spatial Audio line? They have distribution in Europe which may end up being less costly than shipping from the US. I own the M3 Turbo S which create quite an immersive experience due to the open baffle design.

The ATC 20SL passive, right?  ATC 20s have an extremely high resolution driver that shows off amps and cables to a very high degree.   The do start rolling off around 90-85Hz or so, but have the ideal 12dB/octave sealed box LF which can produce quite deep bass if it's there in sufficient quantity.  One octave below 85Hz = 42Hz 12dB down..... Can often be better than bass reflex ports or passive drivers which are tuned up around 85Hz which would be down 24dB/octave after the port.  So 42Hz on such a system= 24dB down.  (It just sounds like more bass than a sealed box because the higher bass is boosted and fools the ear).

I'd try a different larger amp.  20SL's can take up to 300W each and amps at that size can have a much better low end.  I know in my test room, an ATC P1 (150w/ch) vs an ATC P2 (300w/ch) on my 19s passives or 20 SL's are quite different even though they are the same design using the same output devices; the larger one sounds much "bigger" and weightier in the low end, more "massive" would be a good description.   

ATC 19 passive and 19 actives (same main driver as the 20SL but in the newer cabinet with the newer ATC tweeter) made it to this years Absolute Sounds Editor's Choice so I think the speaker is okay.  I wouldn't switch it yet, I'd try some different amps/electronics and maybe cabling.

Brad
ATC USA
Lone Mountain Audio
   

Mundorf ATM in the ATC 20?!! Please explain. Indeed interesting.

Thank you very much for your input! I have the ATC on Mapleshade platforms -it helps for the bass that goes down to 35 Hz when I measure in the room with Diracs room correction software and a Beyerdynamic microphone. Regarding the Mundorf AMT, that improved the sound a lot. I used AMT 1908C - it is more or less a drop in when replacing the Vifa tweeter. I adapted the Xover as well. Actually, a fellow A'goner copied my approach and he seems really happy as well. 
I am not sure how to inrease power without spending a lot. I wonder whether I can bridge the JOB225? I read that single ended amps (- = ground) all can be bridged... so I might just add another Job225?

Go for the Ps 12 if your  room is not big enough otherwise get the ps 15 if you have bigger room.my  PS 12 can play big orchestra at ease...