From my experience with the Arro I don't think the speaker would work well in a room that large, even with a sub. I owned the Arro for a few years and used it with tubes and solid state. I don't think there is much you can do to get around the speaker's inherent dynamic limitations.
In addition to auditioning the Sttaf, I think you should also consider the Model One plus a sub(s), assuming you're open to stand-mounts.
In addition to auditioning the Sttaf, I think you should also consider the Model One plus a sub(s), assuming you're open to stand-mounts.