You might want to take a look at this thread, specifially the specific comment the link goes to. I record some sample comparing the two. I don't like to say that they are exactly the same, but I think the HD500 can be setup in a way that it comes very, very close to the M13. I just think the M13 is still a lot easier to use.
Thnx a lot!
For me the reason to make the switch is turning two pedals into 1.
And because effects between M13 and the XT Live differ a lot. So no use for me to fondle away at home with al kinds of effects only to come to the conclusion i can't use them on the m13. (or they differ to much).
I've watched some instructional videos. In one I noticed that in the HD500 you will still have to select an output mode. In my opinion things went wrong with the XT live at that point. (sound drop)
In that case the M13 indeed is the better in usability.
I also wonder how the HD500 works with MIDI. I use the m13 now to switch channels on my amp. Is the HD500 similar in use in midi controlling? (or maybe even better).
One thing the m13 lacks is interscene spillover. Is the HD500 capable of that?