The Sub wants to make a direct 5GHz connection to the Amp, whether the system’s in SonosNet mode or WiFi mode. A Boost won’t help at all; it’s a 2.4GHz device.
If the 5GHz connection fails your only hope would be to wire the Amps and the Subs, so they could use a low latency wired link instead.
Could I use a wifi bridge? Would that trick the sub into joining the wifi? If this were the case would the sub use the wired link to get the the amps (amps would still be on wifi)?
You'd create a nightmare. The WiFi bridge would make the Sub think it was wired, probably triggering SonosNet for the entire system, and a home theatre satellite must not be wired unless the master player (the Amp) is also wired.
Even if SonosNet was not triggered, the latency variations on the path between Amp and Sub would almost certainly cause periodic dropouts.
Why do you have two accounts here? It contravenes the community rules.