There is also a book on the 6th Tennessee Cavalry (US) called "Hurst's Wurst: Colonel Fielding Hurst and the Sixth Tennessee Cavalry USA" by Kevin D. McCann. It came out in 2007.
The author was in the same boat - thought he had a Tennessee Confederate ancestor and it turns out he was a Unionist. Hurst and much of the unit was from McNairy County along the Tennessee River. A very controversial unit too - Forrest hated them and so did some Union commanders.