I read (or heard) somewhere that it's better to give a dog a two-syllable name, to help them recognise it more easily - sort of, to remove any shadow of doubt from the dog's head that it's their name. I think it's for training purposes. Of course, it's quite possible I'm talking out of my bum on that one, or my source was.
Going off that (rather shaky) theory, then Kyle's out, unless you call him Kyall. Or Kylie.

I think Billy's too common for a boxer.
But I think boxers are of German origin, so why not go for a Germanic name? I looked some up:
Baldwin means "noble friend",
Bamard means "brave as a bear",
Bannan means "commander"
Barnard = "strong as a bear"
Berit = "intelligent"
... and there's many more. Once you get the dog, he might even show some personality trait which will lead you to a name. Post a pic when you get him?