As you plan your system, I think you should separate the power distribution and polarity switching functions from each other. The DB-150 is primarily intended for additional power, the fact that it can also function as an auto-reverser may or may not be helpful in your situation. When planning power distribution, you should try to divide your layout into two districts that will each hold roughly half of your power-consuming trains at any given time. If it happens that your stub terminal qualifies to be its own power district, then it might make sense to feed it with the DB-150, and simultaneously use it as an auto-reverser. But given that there are only 6 tracks in the terminal, it's hard for me to imagine that you'll draw anywhere near the 5 amps that the DB-150 can deliver, even if it's loaded up with lit trains.
Regardless of what reverser you use, you'll still have to wire the terminal feeders according to the above diagram.
