@Chaz54 

Yes.  The EAP225 can be connected to the GX90, but you would need a POE injector to power it as the GX90 does not support POE.  Additionally, the EAP would create a separate network as it does not have an RE mode and is not compatible with OneMesh or EasyMesh technology.  Also, the EAP225 is a WiFi 5 device so it would not benefit form the WiFi 6 features of the GX90.

If you are looking at expanding the range of the GX90 you would be better off using a range extender like the RE815XE and making use of OneMesh to create a Mesh network between the two devices. 

  @Carl 

The EAP225 does have it’s own POE Injector and we have been able to create its own network as you suggested.

It works like the “Traditional Router with Extender” illustration shown on the RE815XE webpage. As long as you have “auto-join” set on your device, it will switch (after a bit of a delay) between networks. What I'm wanting is more like the “OneMesh™ Router + Range Extender” illustration.

To give you a little more explanation of what I'm dealing with, we have a 2400 sq. ft. house with a three car garage. The garage has a suspended floor and I have a workshop below the garage. Therefore the workshop area is totally isolated from any Wi-Fi signal due to the concrete and metal in the floor and walls. I have a Cat-6 wired network throughout the house and into the workshop.  

So based on what you are recommending and from what I have read about the RE815XE Range Extender, I should be able to just plug the RE815XE into the network and I should have the same network access in the workshop. Correct???

  @Chaz54 

To eliminate confusion for anyone else who may be reading this the EAP does not have an RE mode so the relationship with the GX90 would be more like connecting a TL-WA3001 to the GX90:  A physically connected device that provides a wireless connection but gets its IPs from the router.  The delay is the drop from the GX90 and connection to EAP225.  Similar to dropping off your home network to your phone's cellular.  

For the want that feature is actually there but it is a bit more complex with SMB products.  our EAP line, for the most part, supports an AI Mesh, but it requires the use of the Omada Controller.  This can be a physical device or the software version of the controller.   Additionally, it requires more EAPs.  Like Deco, our EAP's mesh is only compatible with other EAP products.   At this time EAPs will not support OneMesh as that is a feature of our Home product line,   

For OneMesh with a device like the RE815XE, it would require a bit of configuration so it would not be as easy as plug and play but it's a simple process. 

Check this Video or this FAQ