Thank you for your advice Fastus, I understand your point of view. Sure, I can buy the Z3000 on AH, moreover I contacted them to see the postage and it's quite interesting. But I'm afraid of 20% in customs tax receipt. In this case it is more interesting to buy in the EU.
Regarding the WMD / SSF Spectrum, you're right: no details on the official site!
It is only classified as "analog" on Schneidersladen and London Modular (http://www.schneidersladen.de/en/wmd-ssf-spectrum.html https://www.londonmodular.co.uk/shop/spectrum/).
Regarding the K3021, I find no information either good or bad, this module is relatively new.
Btw what do you think of Malekko modules? I saw that you have the Anti-oscillator.