@VeryConfused Hello, 

In theory, all the TP-Link powerline devices on sale can work together. In the real network environment, it would be better if we use the powerline devices with same powerline data speed in the same network. We can also use powerline devices with different data speeds together. Here are some recommendations:

So you could consider 8/4 series as powerline extender(s),  here is a FAQ that may help: 

https://www.tp-link.com/support/faq/2725/

How to add another powerline extender into existing poweline network: 

https://www.tp-link.com/support/faq/1615/