Another strange discovery that I've just made...I was able to send a signal to the stereo hub via Bubble UPnP app on my phone.
When I go to the jriver folders on the app and select a track, I see it playing also on my pc and the Buchardt speakers are selected (Please see attached screenshot)
Interesting indeed and something I was wondering about but was "afraid to ask".
Your Platin Stereo Hub advertises Chromecast Built-in as one of its wireless input capabilities. The BubbleUPnP Andoid App is very robust and excels at making Chromecast devices available to MC as DLNA zones. In your case, it is apparently detecting the Buchardt Chromecast renderer. The Bubble app can use MC as a music server, so it should reveal on the phone most or even all of your normal MC windows and library whenever the MC server is running.
If you tap the chromecast icon (middle right edge) on the Bubble Android App, you should see the Buchardt as one of the available renderers, along with "Local Renderer" which is the phone itself (LG-H990), and you may see the MC Server PC also available as a renderer.
I am always running BubbleUPnPServer (different from the Bubble Android app) on my MC server computer. In this case, Wireshark captures SSDP NOTIFY alive packets on the ip (wireless) interface, labeled with
Server: Windows10/10.0 UPnP/1.0 BubbleUPnPServer/0.9-update41\r\n. These packets enable Chromecast discovery as a DLNA device by MC. With Bubble Server, MC treats these as full fledged DLNA zones and so it can play to them even without the Bubble Android App running, something you may want to consider if the direct DLNA issue does not get straightened out. The zones created with BubbleUPnPServer appear with "(DLNA)" appended to their name.