Ok, thank you.
I can't find the alpha version of the Motherboard Asus, is it better to take the Zenith Extreme (no Alpha) or the MSI Meg creation?
Non-alpha, the original Zenith Extreme,
not under any circumstances. You would have to buy additional 10 euro 40mm cooling fan kit Asus sells and it would look hilarious, and both VRM and chipset cooling would still be pretty bad.
If you don't want 4xGPU in future (in which case Aorus Xtreme is the only board that supports doing so), then MSI MEG. Reason why Alpha and MEG can't have 4 dual PCI-e slots is because those big VRMs don't fit even on regular E-ATX board together.
Where are you from ? There are plenty of Alphas on Amazon in US and EU when I checked at least. The 10Gbit onboard plus Asus UEFI (much nicer than MSI's...) are big benefits for going for Asus, but from hardware standpoint, MSI's VRM is still superior.