Since many Zephyr and Zephyr Xtra Starter Sets are used on smaller railroads, a natural choice for setting up an automatic reversing section would be an AR1.
If you have more than one reverse loop, then the PM42 is a better choice.
These automatic reversing strategies will work equally well for any Digitrax system using any Digitrax Starter Set. Alternately for larger railroads, an auto reversing booster such as the DB150 can be used for automatic reversing if the section is large.