@MixBix 

You can add a range extender to boost the wifi signal, while cause they connect to each other by wireless, the performance depends on the actual network environment, including distance, interference, obstacles. 

For the single powerline extender, per you know, you can buy a single TL-WPA8630P , without the wireless connection interference, the connection quality may be better, while the price is what you may concerned; 

Therefore, it is up to you; both devices have their pros and cons. 

Good day. 

@Kevin_Z 

Can I use any of the TP-Link extenders for that? Would be good if I could monitor/setup both the existing devices and the new extender(s) via the one dashboard.

@MixBix 

You can use the TP-Link extender to boost the wifi signal; cause the TL-WPA8630 is dual band, you can order a dual band extender also, like RE200, RE350, RE650.

While the extender cannot be managed via tpPLC utility, instead, some extenders support Tether app which we can use to monitor the extender, besides, it has own web UI.

Or you can login to the web UI of the main router to detect the powerline adapters and range extenders which are in the same local network.

May it help and have a good day.