Boost coverage

You can add as many boosts as you desire, up to a total Sonos device limit of 32. Additional speakers also act as Boosts, so if you found that you needed something between speaker 1 and 2 at opposite ends of the house, a play:1 would work just as well as a Boost halfway between them, and give you the benefit of more music :)

You can always choose to wire your devices directly to your router as well, rather than relying on your local wifi signal, it that's a possibility.

My house has thick walls and wifi signal is always an issue,
Using wiring to the units is the solution in such cases; Boost is good, but still can't beat these issues.

Thank you for your answers.
Does it always have to be wire connected to the modem? Or could it also join and expand the network through wifi, just like an airport express?

Will a Connect:Amp also act like a Boost?

Yes it will, once wired to the router.

Thank you for your answers.
Does it always have to be wire connected to the modem? Or could it also join and expand the network through wifi, just like an airport express?There has to be a Sonos component wired to the router. When that is the case a Boost can act as a repeater for your Sonos devices as part of SonosNet. It will not extend your wifi network.

If you don't have a Sonos component wired to your network then a Boost located elsewhere is completely redundant.