@moorsider 

Single Deco P9 will not connect with the rest of M5 Deco mesh over powerline. P9 will not connect to TP-Link AV1000, too.

There is another option, which you can actually test before buying additional hardware. Deco M5 can use TP-Link powerline adapter to establish Ethernet backhaul over powerline. Which means, if you bring Satellite Deco M5 to the cabin and connect it to AV1000 adapter with Ethernet cable, M5 could establish Ethernet backhaul.

For that to work, one of powerline adapters in the house must connect to Main Deco M5, or to switch that connects to Main Deco. If you have that already, take one of Satellite M5s you already have and try it in the cabin.

If that works, buy additional M5 unit to complete the WiFi mesh setup. 

@Alexandre. Many thanks for your quick reply - much appreciated 🙏🏻

This sounds like it might be the best solution; the Deco M5 system is already linked to the cabin over the powerline adapters (and that works), so as long as an extra M5 unit could use the powerline backhaul, we could have the same WiFi login in the cabin as in the rest of the house.

Time to go looking for another M5 unit... thanks again!

Follow-up... I took one of our "satellite" Decos out to the cabin, and connected the AV1000 powerline adapter (already out there) as a backhaul.

I'm happy to report that it works the way I hoped it would 👍🏻 It made the cabin a part of our home Deco network: the link is not exactly speedy (I got about 50Mbps up/down, compared to about 300 over WiFi in the same room as the main Deco, and nearly 800 (!) with a direct Ethernet connection), but that's almost certainly down to the powerline adapters. (I've been pretty disappointed with the performance of the AV1000 adapters in our house, and wonder whether there's interference in our wiring or something...)

That said: I sometimes use the cabin as a "backup" office, and the network speeds I got out there should be sufficient for Zoom/Teams calls and the like. Many thanks again for suggesting an extra M5 unit 🙏🏻