@Willferox 

If you happen to have a surge protector you can try putting the powerline on that to see if that may help filter some noise. Other than that since you already have an Ethernet cable ran, you could probably use any simple access point go broadcast Wi-Fi.

@Tony 

Thanks - an access point seems to make sense. But do you know of one that has an additional Ethernet input allowing my to hard-wire my computer in addition to providing a wireless signal?

@Willferox 

You can get a cheap simple router and set it up like an Access Point. Run the cable providing internet to the LAN port of the device, so you can then wire to the remaining ports and the network device will provide a wireless connection.

Here is an FAQ that shows that: https://www.tp-link.com/us/support/faq/417/

What is the internet speed you get when you wire your computer to that cable and do a speed test?

@Tony 

about 200mbps

@Willferox 

So in that case any router that has gigabit ports or 1000 Mbps LAN ports.

@Tony 

Thanks Tony, but is there any assurance that an access point wouldn't interfere with my speakers as my current unit does (even when not using the electrical mains to transfer data).

@Willferox 

An access point doesn't use the electrical wiring like powerline adapter do so not I would not expect it to interfere with your speakers.