What happens when you remove the splitter? 

I’ve actually just done that to see what the audio source is. HDMI cable direct to tv I’m getting Dolby 5.1, through the splitter i can get 5.1 but only the one tv at a time. 
 

A bit of background. I have a cheap Chinese splitter that allows me to watch on both tv’s simultaneously at 5.1 and on one occasion even in atmos(although I’ve never seen anything else in atmos from virgin). I wanted to swap this because occasionally I’d get drop out and even white noise until I rebooted it. So I assume my set up and all the leads are good. 

An unpowered splitter would likely drop the voltage of the HDMI signal, which would then depend on the quality of the TV’s circuitry to pick up enough to present upyou with both a full 5.1 and ARac. I suspect there’s something going on with your ‘cheap’ splitter. 

I’d consider a more expensive splitter that is powered, or an actual HDMI switch, rather than splitter, but of course, that would be powered to ensure the full signal gets sent to each TV. 

This is not a Sonos issue.

Both splitters are powered. I know it’s not a Sonos issue I was just wondering if there was any settings I could change to resolve the communications issue when both outputs are in use 

Your best bet would be to contact this Nikkai customer service, and explain the issue. Or even the TV manufacturer’s CS.  There isn’t any settings in the Sonos system that would help this. 

When a source (virginmedia) is connected to a TV via HDMI, the TV has to communicate back to the source what sort of video and audio quality it’s capable of, so that the source will send it the best quality it can plan.  In the case of audio, your TV will get the quality it can play from the connected soundbar.

So when you actually have 2 TVs connected through a splitter, the splitter has to communicate to the source as if it was a TV.  Some splitters, you can manually the audio or video quality.  Some will take the lowest common denominator of the TVs connected. The better splitters/matrix can take the higher quality and downgrade to the lower quality one of your TVs may need.   It sounds like the splitter you have is just not handling this well when there are two sources.  You might want to look for a manual switch on the device, but that will likely limit the audio you can receive, or maybe see what the device manual says.

What are the length of the HDMI cables here from the Nikkai Splitter to each TV? If it’s quite a distance then perhaps see if an ‘active’ HDMI lead will resolve the issue, rather than using a ‘passive’ HDMI cable. (Note: An ‘active cable is one-directional only).