Although you have to use Sky's router to connect to their service, I cannot see any reason why you cannot plug either a "Cable/DSL Router" (which *DOESN'T* incorporate a modem) or a Wireless Access Point into one of the Sky router's LAN ports. If it can allocate addresses by DHCP to connected computers, then it can allocate them to a secondary router's WAN port or a Wireless Access Point.
Alternatively, as you've suggested, Powerline adapters might be a solution, at least as far as the "other end of the house" is concerned. Connect one by ethernet cable to the Sky router and use a WiFi Powerline adapter at the other end where wireless connectivity is required. The fact that you're using a Mac is immaterial.