Following our report about Rockman Xover's latest update, you can have a listen to the original theme for the new Battle Arena mode above. Although this is not officially announced, to my knowledge, it's presumed to be composed by Masahiro Aoki, who who also created the game's main theme. You can read more about his involvement from our translated interview.
Thanks to Django Ringo for bringing us the tune! You can download the MP3 here.