@Gravoren Thanks for detailed info, it is very helpful. Drawing is fine, too. I want to ask you one more thing, and this will be it: I'd like to know firmware version of your Deco X10s. You can find...

@thelinkuser You can plug Main Deco PX50 to TL-WR940N. When doing initial configuration of Main Deco, select "Dynamic IP" type of connection. This will force Main Deco PX50 connect to TL-WR940N just...

@Morgens You will need to keep X90 as Main Deco if you want to continue to use HomeShield. It is also important that M9 Plus has the latest firmware. Please share Update Deco page screenshot from...

@Gravoren Any one of these will work, but each has its own caveats and requirements. You need to provide more info to get better answer: Do you have switch already? If yes, what is its brand and...

@Ant_ See How to extend guest network when there is a switch between Decos Follow Topology 2 (two or more satellite Deco units) section of that document.

@BigKevOz D-Link switches are known to have issues with Deco Ethernet backhaul protocol. You may need to replace switch by different brand, TP-Link switches are usually safe bet. Check this FAQ...