Just downloaded and tested the demo. It works on my DM500, and I'll buy the full version soon.
1. You may already be aware of this, but the DM500 (and possibly 600) has slightly different button mappings than the other Dreamboxes with the larger remotes. In particular, the DM500 doesn't recognise the command issued by the Info key. It's the same with the remote on the web interface (I guess that's where you get the commands from), so it's not your fault and it's no big deal for me.
2. There are a couple of small UI aspects that you could tweak. For example, the menu item with label 'search for help and support' is all lower-case, which is out of step with the other menu items. Also, I would probably use the placeholderText property for the remote title when none is set. That way, when the user taps on the TextEdit component, they don't have to delete the 'Remote Name' string before adding their own. It might also be a good idea to do the same thing for the IP address, so you don't have to delete the zeros.
I do also notice that there are some cases where you don't appear to use the 'standard' components. For example, the dialog that is raised when you want to delete a remote does not use the standard QueryDialog component (see screenshots below). I think it would help give the UI a more consistent look and feel if you used the standard components where possible.