Here is the unit history of the 6th Tennessee Cavalry (US) from the Tennessee and the Civil War website:

http://www.tngennet.org/civilwar/usacav/usa6cav.html

Your ancestor is listed in the Adjutant General's Report here:

http://www.tngennet.org/civilwar/rosters/cav/cav6/coa2.html

Here is some more history of this unit:

http://www.tngennet.org/civilwar/rosters/cav/cav6/memo.html

Hope this helps,

Jim Martin