1. Daisy-chain mesh should work in AiMesh, but the platform isn't as optimized at handling multi-point topologies as other purpose products.
2. They should still communicate in a daisy chain, yes.
3. The setup would likely be less than optimal for the 88U (at the very least), as it's only dual-band, so it would be using its only 5Ghz radio for backhaul.
4. AX alone will do nothing to increase signal strength.
5. Suggestions below:
Instead of plunking down $400 USD for a 2-pack of AX92U's, first I'd want to know if there is any possibility of wiring even just the base router and first remote unit to one-another, if not all units? If not with ethernet, than how about MoCa over coax? Either one would solve a ton of would-be issues right there, and ultimately allow for the operation of AiMesh with better results, even if only one hop was wired.
If that was a no-go and you simply must run wireless backhaul and multi-point, I would honestly consider a different product altogether, especially if you're ready to drop $400 (or more?) on the setup. If you're more of a novice, something like Netgear Orbi or Eero Pro. Orbi is tri-band for more potential client and backhaul bandwidth, but Eero Pro has had multi-point support baked in from the beginning (Orbi only added it recently so the code base is young and likely a bit buggy), and Eero has more well-developed packet flow management. Beyond that, if you're more skilled and don't mind dual-radio architecture, working-pull/overstock enterprise gear is the way to go; Aruba Instant or Ruckus Unleashed are tops in that area. Regardless of your preference, any of those choices will be a better pick for multi-point mesh.
Lastly, a passing comment on on 802.11ax. In short, I wouldn't. Instead, just run proven AC Wave 2 gear. AX isn't even ratified yet, nor are its truly differentiating features even enabled, let alone functional, on much of any real gear in the wild (stations or clients). That said, I do tend to value practicality and reliability over bleeding-edge features (or not-yet-realized features). But to each their own in that regard.
Thank you for the quick reply!
1. I am still learning about AX and its hard to find reliable guides and tests about the technology yet.
2. The reason I asked if it would work in a daisy chain is because I found a post that said, AiMesh supports up to 2 nodes in daisy chain, but it is not clear to me if it is 2 AiMesh nodes in total or the main router and 2 nodes. Asus doesn't really mentions that.
3. The 92U uses tri-band, however the AX standard is only supported on one.
I don't know if I'm right, but my theory is, it would use the AX band for the backhaul and the AC band to communicate with clients.
While the 88U should still have enough bandwidth to support AC clients as well.
4. So it seems Asus uses some misleading marketing BS here, claiming that AX has "better coverage" compared to AC
https://www.asus.com/us/Networking/RT-AX88U/
Anyway the 92U should have a better range than the Lyra mini. Right?
5. Wiring is not possible. The walls are thick and isolated, absorbing most of the signal. I already experimented with different options, like powerline, and the AX seems basically my last hope to make a reliable coverage.
The 92U would cost $370, and I would sell my Lyra mini for about $180.
The reason I started building my network with Asus networking devices is because it has nice features and hardware accessible on a relatively low price. Fairly good IDS/IPS (that would cost me a lot to buy separately), initially I used its external drive features before I had the money to buy a NAS, free DDNS, etc.
I know Asus is not the most reliable on the market, but gives okay overall features/performance at a good price.
Now it would cost too much to replace the whole system with another brand. Hopefully the software will improve with time.