Great find! I have a nice old Regal Tenor guitar from the thirties. I've strung it many different ways, and it's a neat instrument to play. I guess the two most famous "folkie/country" tenor guitarists were Nick Reynolds and Rabon Delmore. Both played Martins. The reason that yours is not louder is that they were braced for heavier strings. Try a set of tenor strings, and you'll probably hear quite a difference.

Rick