Can I use a satellite from RBK23 to extend my new RBK853 Environment

[EB2]

I recently purchased the RBK853 for my home and I'm replacing the legacy RBK23. The 850 series does a good job of maximizing coverage across the home; however, there is one area i want to extend wifi to and it does not have to perform at the same speed as the other satellites. Is this something that's even possible or do I need to pick up another satellite to extend? 

[CrimpOn]

The satellite from the original Orbi will  not sync with the AX series Orbi's over WiFi. The radio chips are different.

I have seen comments that they will sync over an ethernet connection (which is not practical most of the time).

Orbi AX satellites are not cheap.  If this area needs to service devices that do not move, a WiFi extender of any brand could extend coverage for them.