Hi Greg,
This KB page on Roon Architecture may assist.
Roon Server is pre-installed on the SonicTransporter. This is why Roon didn’t like you installing another Roon Server.
The Sonic Transporter will be your Core. No need to install Roon Server anywhere else. All audio signals will pass through the Sonic Transporter.
Install Roon on the Dell Desktop, point it to the Core on the Sonic Transporter. This is a Control, sometimes called a Remote installation of Roon. You can now use this version of Roon to configure the Core and create Watched folders where your music is stored. Roon works best when the storage is located “close” to the Core (eg: an SSD on the Sonic Transporter or USB off it) but can work by accessing network storage (such as the Vortexbox). The thing to remember is that all audio goes through the Core, so with network storage files are retrieved over the network to the Core and then music is sent over the network to any network zone. This real time duplex is fine with wired Ethernet, sometimes not so good if any part is Wi-Fi.
Controls can be Wi-Fi, the music doesn’t actually go through a Control unless it is also being used as an Output.
You can install the Roon Remote app on your iPhone, and point it at the Sonic Transporter, it is now another Control that can configure your Core. You can have multiple Queues to different Outputs controlled through either Control simultaneously.
Now let’s look at Outputs. Every Control will see all Outputs which are either network zones or connected to the Core or a Remote (unless configured as a private zone exclusive to that Remote). The iOS apps don’t have an Output (yet). So you can directly connect DACS or DAC/amp integrated devices either to the SonicTransporter or your Dell using SP/DIF, Toslink or USB.
If you want to connect to a device over Ethernet as a Network zone with RAAT then it needs to be either Roon Ready or running Roon Bridge. Roon can also connect to Airplay, Squeezebox or Meridian Network zones, but not Devialet Air or UPnP/DLNA.
Your micro-Rendu has Roon Ready pre-installed as an app you configure through the SonicOrbitor software. All your Roon controls should see the micro-Rendu as a Network zone when the Roon Ready app is selected and a USB DAC is connected to the micro-Rendu, switched on with USB input selected. That could be either your Devialet or the Audio-gc.
Unfortunately the Devialet Amp is not Roon Ready, so it will not appear as a Network zone. You can either connect it directly to the SonicTransporter or Dell, or use a network zone device (such as the micro-Rendu) to connect to it.
There are quite a few Roon members with Devialet gear who have been lobbying Devialet to implement a Roon Ready solution through firmware. So far that has not been successful, but there may be some workarounds using Squeezebox (which Roon can see as a Network zone) that I am not familiar with. Let’s ask my fellow @moderators and Steve @hifi_swlon who might best be able to guide you there.
Hope the above helps clarify things.