It sounds like the MTH explorer for $150 and a power supply would be the least expensive option to run a subway set with Proto Sound 3. I assume all the functions would be on the app.
EDIT: In looking over past posts regarding the Explorer and subway announcements, it appears that a combination of the MTH Explorer and the app will NOT work to trigger station announcements. That means a very expensive TIU and WiFi setup is the only option.
Can anyone confirm this?
John