All I can see is that the 9th was south of the Burnt Creek road in Jackson's Division. The map I have looked at is the one in Wikipedia. The 9th went on line and held a division at bay all day. It had replaced Ferguson's Brigade. A regiment replacing a brigade, Cavalry fighting as Infantry. This was the 27th of June 1864.
I can not see which division/brigade held the 66th. The 9th was trained as Infantry and fought as Infantry at Corinth and Hatchie Bridge. They would put one man holding 5 to 6 horses and go into the line.
Grissom in his diary describes the band playing at night but does not single out the French horn. Grisson describes a visit with Terry's Texas Rangers in the same area.