I have been using the test funtion in xlights to set the proper color order for the different strings I am using, with the etd to f8 and 16s ssc, and uscs. When you are making your tree model are you setting up each string for each ssc with the proper start address for each. That I know of you cannot set the start address for only 1 ssc and have xlights know that you are using ( lets say 8 sscs) individual controllers. Each ssc is its own controller with its own start address. I can tell you from experience if your model is not set up correctly with the controllers it will not work. You have me stumped on how you can get output out of the fpp to etd to hub to sscs by converting xlights but you cannot get xlights to play from computer. I used lsp for years and xlight is 10 times simpler to set up for output..
Try this: put you fpp in bridge, make sure you have the e131 output box ticked, in xlights make sure you have each universe activated as yes take your model and put it in a new sequence, you dont need timing marks, throw an effect on your model, I would use something more defining like spiral or bars, click on the effect so it shows in the model preview window an hit output to lights.If you controllers are set up correctly you should have light. This would be the exact same info you would be converting to the fpp that you say works using fpp to etd ect. You dont even have to hit render or save. I just hooked up my etd istead of my fpd and did this just a few minutes ago, and have been doing it for several days so I can adjust my effects visually before I put them into a sequence.
Joe