@carlesp 

-Buy another RE705X, set it up as access point next to the MR600 (wired). Create a mesh with both RE705X (is this possible)?

Do you mean a network topology like:

Archer MR600---<cable>---1st RE705x ) ) ) ---wi-fi---( ( (2nd RE705X

RE705X does not support OneMesh/EasyMesh under Access Point mode.

So if you still wish to have a Mesh network, I think a 2-pack Deco S7 will be better, or you could also consider the Wi-Fi 6 Deco, like Deco X50.

Deco Mesh roaming performance will be more smooth than OneMesh.

For the topology, Archer MR600(Wi-Fi disabled)---<cable>---first main Deco S7 ) ) ) ---wi-fi---( ( ( second S7

Since Deco S7 also works as a router by default, you could put Deco S7 into Access Point mode and the Mesh network could still work properly.

Thank you very much and best regards.