ATC scm 19 vs ATC scm 20SL?

I own an ATC SCM20 SL since 1992. It is the oldest piece in my chain. I had a love-hate relationship, but I am glad I kept them. While they provide a rather dark, mid-hall sound, they brutally reveal any weakness in the chain. They are especially sensitive to any sibilance and "digitits".
I modded them heavily, with all Duelund crossover components, ring radiator tweeter and C37 lacquer. They are unique in combining intimacy with force. The Quad ESL63 had a similar "intimacy", while seriously lacking force.
I am happy now, driving them with Nuforce 9V3 SE, Metrum Octave dac, Audiophilleo2 and ASI liveline cables.
My dream amps would be Spectrals though...

How can you do a driver swap without destroying how they were originally voiced? I don't want to sound too critical as I have done this very same thing with 1985 vintage ProAc's. The tweeter replacement was from the Response series (i.e. one silk dome for another).

@ Linkster
The two tweeters (Vifa D27TG and Scan Speak D2905/9700) share the heritage, and the impedance curves are almost the same. So it was a drop-in, besides adjusting for the slightly different sensitivity. This was also confirmed by a professional who designes Xovers for loudspeakers. I was never very impressed by the sound of the original, cheap Vifa tweeter, and I never regretted the exchange. ATC seems to have recognized the weakness of the original Vifa tweeter as well, as newer models use a much better Seas tweeter.