Hi there!
When I bought my HD500X I did not get good tones out of the box. After a while I did manage to set it up for great tones with simple tips I found here, on youtube and on Line6 instructions. So I think the list bellow will help you to create great tones:
1º) Use direct/studio output when Phones, XLR or 1/4" Out is being used.
2º) Set the mixer L and R mix to Center on both sides. (Great improvement here)
3º) Select the amp you want, set the Channel Volume to Maximum and work the other parameters as needed. (this will help to make the amp sound better and also normalize the presets volume outputs for better matching volume between presets).
4º) Use the noise gate first in chain, default setting is most time enough to kill some noise when playing high gain.
5º) Try a compressor before and after distortions, it helps a lot to get a good tone when you feel something is missing.
This is what did the trick for me! :D