Extending R7800 5Ghz signal

We have Virgin media for broadband but their superhub 2ac router kept dropping the wifi signal (annoying with Nest cameras) and I would have to reboot it every few months. I've since put it in modem mode and attached the R7800 which I love. Solid signal. Almost no downtime (I've had to reboot it once since I bought it in April).

Downside is 5Ghz signal. We live in a 3-bed semidetached house. It's small but with solid brick walls. Wifi through one wall or floor is fine. Through two, the 5Ghz signal is almost absent but the 2.4Ghz is good (although slow). I want to boost or extend the 5Ghz signal.

No option for ethernet backhaul until I redecorate (maybe in 5 years!). I've got powerline adapters in order to set up a NAS in the garage. The EX7500 and EX7700 have mixed reviews on Amazon. Do I go for one of them, more powerline adapters, another R7800 as an AP or something else?

 

Hey, I know the solution you are looking for is an indoor type. But 2 weeks ago I just installed a Hawkings Technology H0A12DP. It's a directional antenna that attaches to one or two of the antenna ports on the router by cable. It extends 2.4/5ghz a/b/g/n/ac. I installed mine with a 30 ft and a 7ft cable all purchased from hawkings technology. with cable and atenna cost me around $115. It works amazing. I bought it to get coverage from my house to my guest house. I have the ex8000 nightawk extender which has gets a great signal from my r7800 on 2.4 and 5ghz and its 300+ft away. I am surprised how great this thing actually works. So while this might not be the solution for your issue I would definitely check out their other products on their website because they are amazing.