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.

My room is nearly 5x3 m .. I'm not sure if it's big enough for scm 40 

The SCM40 will work fine in your room assuming have the time, patience and skills to properly set up speakers and listening position.

Jim Smith's Get Better Sound book is a great guide.

op

no commentary on what you are trying to improve in the upgrade?

if the mere objective is to buy the more expensive bigger model then that mission is most easily accomplished...

anyhow, there are many paths to hifi happiness, wish you best on yours

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.