You could try the usual solution of a Powerline Bridge and a router configured as a WAP. It's basic networking so I'll give the search about the router as a WAP and stop there. Why? Because I've found extenders to be so hit and miss that I no longer use them.

-> https://www.google.com/search?hl=en&as_q=how+use+a+router+as+access+point

Recipe?

Your SBG6580 -> Powerline Bridge -> other Powerline Bridge in a central location for the router as a WAP.
Bob