ATC Scm 19 V1 Upgrade or what?

I agree with VV. I think your best bet is to go to the passive SCM 40 V2 with the ATC amp you already have. It will be just fine driving the bigger speaker.

An additional thought. While some might prefer the extra detail in the 19s, many would agree that the 40s represent an overall improvement to the sound, depending, of course, on the room and all the other variables. This strikes me as a valid point of view, even if I disagreed with it.
To be fair, I may be overreacting to past posting trauma when others were unkind to me after I asked stupid questions (and they were).

From the OP's post, I assume he means a wholistic or general improvement to SQ (to his ears). Sure, some of us could better help him if he had something specific in mind, but I know my orientation/understanding doesn't always afford that when I ask a question on here. (Which makes me equally annoying to some, I'm sure).
Anyway, if we can offer help on the OP's terms, however limited that may be, it's still help. 
Of course, it's also a form of help to let the OP know that specifics are really useful in question asking, especially about what would improve a system.