Stay with the Kef R3. Later add subwoofers. I insist on the plurals.
The FR curve you just showed us, for the Z2, although very smoothed is not as good as that of the R3 ... I would daresay that the Kef R3 is an objectively better speaker. Actually, ... no dare necessary : D
As for amplifers, the EC-1 has no glaring issues and as such, will drive drive the Kef R3. I would advance that nowadays there are less expensive and objectively better options. These options although better objectively may not bring any sonic benefits...so... You will come to see that the issue of electronics (DAC, Amp, etc) is virtually solved. Transducers and the room in which they are placed remains the issues.
Do know that it takes time to get the best results from any system. Do not be seduced by the siren song of some speakers: They sound fantastic until you get used to their sounding, "fantastic" and start noticing that they sound wrong, since they sound "fantastic" on anything and everything, including pieces that shouldn't sound "fantastic"... I will go out on a limb and put numerous Klipsch and Monitor Audio models in that category.
Keep the Electrocompaniet ECI-4
Get the Kef R3
Get a miniDSP Umik-1
learn to measure. Takes a while but it's fun.
Return here for advices, questions and suggestions.
When you are ready for subwoofers , acquire a miniDSP 2x4 HD/
Add, at least, a pair of subwoofers from reputable manufacturers, you are in Europe thus would suggest to look for European manufacturers. Subwoofers are relatively big and often heavy ... thus shipping charges can be serious.. @sweetchaos
has put together a superb tool to choose subwoofers.. He's put together more tools .. Thanks @sweetchaos
. Here is the Sweetchaos Subwoofer Comparison
In a medium sized-room up to 30 square meter, the Kef R3 + a pair of good subwoofers are as good as it gets for accurate and realistic reproduction of any type of music, from EDM to RAP... passing though Western Classical, Baroque, acoustic Jazz, Vocals .. etc.... From 20 to 20,000 Hz at any healthy Sound Pressure level