I agree, you'll likely need a compatible harness or interface to connect the new unit properly while retaining the oem system's power and speaker connections.Hi there! You might be able to use the OEM stereo's aux input, but it depends on how the NAV system was integrated. In many 2014 SE models, the aux input is routed through the NAV unit, so if that's been removed, the aux might not function unless you rewire or use a bypass harness.
Have you tested the aux port with a device yet? If it's inactive, an aftermarket head unit with aux-in could be a cleaner fix.