Okay, it looks like the
Space Tech EMS-200 basically replaces the functionality of JRiver Media Center running on a Windows PC. Hence, MC is now redundant.
If your Windows PC is located in an appropriate place, close to your Amp, speaker connections, etc., then you could either put your music on the PC, or plug the 5TB Toshiba Cavio drive into the PC so that it is available for MC to use, then plug the
Space Tech DA-DSD1024-8X into the PC via USB, and play from MC to the DAC directly like that. Which means you will not need the Space Tech EMS-200 or Volumio.
If the Windows PC is located away from your music playing area, then it looks like the Space Tech EMS-200 may be able to act as a DLNA Renderer, so that MC could stream your music from the PC to the Space Tech EMS-200 using DLNA, and hence to the Space Tech DA-DSD1024-8X. It could be that Volumio running on the Space Tech EMS-200 is required to act as a DLNA Renderer, which is probably why the manufacturer recommended installing that. If using Roon, I suspect that it would send audio to the Volumio installation, and hence out to the DAC, in the same way. But that solution means that you are hardly using any of the capabilities of the Space Tech EMS-200.
As the manufacturer is saying this can run with Roon, it sounds like he doesn't know what JRiver MC is. I assume he was saying you could install Roon on your PC?
So part of my reason for asking about the location of devices was to answer whether you should ditch the Space Tech EMS-200 and just connect the Space Tech DA-DSD1024-8X and the 5TB Toshiba Cavio drive to the PC, and then use JRiver MC as before. The alternative, if devices are separated and need to be connected via the network, is to run MC on the PC and stream to Volumio on the Space Tech EMS-200 using DLNA.
I know that several people do use Volumio running on various devices to act as a DLNA Renderer for MC to stream to. But I also know a few of them have had issues with their configuration, because of Volumio. So getting a DLNA solution working with the Space Tech EMS-200 may not be straight forward.
Over to you really. Or maybe someone with more knowledge of the Space Tech products, and Volumio, (I have never used either) can speak up and provide better advice.