Hi dcabana
Welcome to the Roku Community!
Yes, both the Roku Express 4K and Ultra support casting over a video wall. As long as your Userful server supports HDMI input and output, you should be able to connect the Roku device to the server and cast the content over the video wall made from 8 TVs.
To set this up, connect the Roku device to one of the HDMI inputs on your Userful server. Then, configure the Userful server to display the Roku content across all 8 TVs in the video wall. The process for configuring the video wall will depend on the specific software and hardware used in your setup, so you may need to consult the Userful documentation or support resources for detailed instructions.
In terms of the specific Roku device to choose, both the Roku Express 4K and Ultra should work equally well for casting over a video wall. The primary differences between the two models are the Ultra's faster processor, additional ports (including an Ethernet port), and support for voice control. However, these features may not be necessary for your specific use case, so the Express 4K may be a more cost-effective choice.
We hope it helps!
Warm regards.
Lianna