If you'll only ever run maybe three DCC/sound locomotives, and they're all in pretty good fettle, I would say two whole amps is all you'll ever need. It does depend, though, on the resistance in the consist behind the locomotive(s). This can come from grades, pinched and narrowed gauge here and there, curves, and poorly rolling cars whose trucks need some tuning. So, the Zephyr is a good bed. If you find, eventually, that you would like more power, simply add a booster in line. I can tell you that you are unlikely to ever want more than 3 amps unless you have guests and run multiple lashups along the mains.