Which router should I use?

[#1]

@Champnet I am not sure if I responded properly to this. They are all connected on SonosNet. I had one speaker plugged into the main router via an ethernet cable but apparently that made matters worse! 

In the sitting room I had another speaker plugged into the TP Link which I suspect was making matters worse.

My Sky box is plugged into the TP link in my sitting room, and that seems to be doing OK.

[#2]

@Dan_the_Van    PS I have chhecked the settings are the same for both as you recommend but I can't change the "wireless mode" which is loing and complicated on the TPLink (something about mixed?) but only Mode 1, 2 or 3 on the Plusnet router. I may be being really dense but I can't figure out how to swap between 2.4 or 5GHz either! Thank you for your continued help.

[#3]

@ellythemoo 

You can not split the Wireless names 2.4 and 5 GHz always share the same, but you can turn either OFF.

To change mode click on the box saying Mode 1; a selection window should pop up.

Some wireless devices you are able to setup your preferred band, setting will be in the device hardware properties.

Depending on device usage 5GHz may not be necessary; a strong 2.4 GHz signal could give you a faster connection compared to a weak 5 GHz

For WiFi devices connected to your WPA4220 would be limited by two factors, the interconnection speed between the powerline adapters and Ethernet port which only supports up to 100 Mbps.

Since moving to Full Fibre I get a interconnection speed on the powerlines of around 90 Mbps, I see roughly the same speed using both Wired and Wireless connections.