Yes indeed. I am attaching my XML to try once more with Unraid, but as you said if this does not work it means there is something else going on when you are loading the Loader.
I added comments to some parts of the XML so you can understand what I am doing, it does not have to be similar to mine. For my setup the key parts to make it work was the USB 3.0 XHCI to boot from the USB, the SATA Controllers which I also had to edit the controller number and the unit number. But definitely start with a single SATA virtual disk for now and then make the rest work and finally I changed my virtual NIC to e1000 when I first started to try this on Unraid.
Also, go and download the loader for the 3615xs or 3517xs (I am not sure about the models if I wrote them correct) the loader is 1.03b and 1.02 I believe and try Unraid on them also. They also worked for me on Unraid. Also on my XML I wrote in the comments that I am passing through my NIC because is compatible. This is not mandatory for you, you can create a virtual NIC with the model e1000 like the previous xml part that I pasted to you. I have a Test 918+ which is like that and it works fine.
If nothing of this work, then if you want to know what is going on I think somewhere on the forum the community is saying that if you are installing XPEnology BareMetal and your board has a serial port, and you have the cable of course you can see what is going on with the loader. It's the only way I believe. I am not 100% sure about this info.
I hope you get a different outcome.