Both Tonal Energy and Harmony Director are GREAT for working on chord tuning and training their ears to hear adjusted intervals like Major 3rds, 4ths, 5ths. You can do this with the simple Pass Through Drill in literally any key.
Use drones working on show music as well. The more constantly you have the drone on the better their ears will get and their ability to adjust will get better as well.
Drones ABSOLUTELY make a noticeable difference in ensemble sound. An absolute must!