The music of that period is not only made of marches but also of very relaxing tunes (some of which are incredibly famous even nowadays) that also help concentration and not only immersion in my opinion.

This morning i looked for more, and i found some that according to me are suitable.
Sources:
http://www.bfv.com/cwb/ <-- Whole set of musics
http://pabucktail.com/Music/Battle%20Hymn%20Sousa.mp3 <-- terrific!
http://pabucktail.com/Music/Going%20Home.mp3 <-- with vocals
http://memory.loc.gov/ammem/cwmhtml/cwmconcert.html <-- 19 samples