Need help hooking "premium audio" radio to base speakers!

[mhardgrove]

I purchased a 10-12 Sentra "premium audio" head unit. It is the one with the 4.3' screen ("PY04F" part number 28185-zt50c). This unit was part of the 8 speaker Rockford Fosgate package, and found after installing into my Versa that this head unit does not have an internal amplifier.

I am a bit stumped, the harness for the speaker wires hooked into the back of the "premium radio" just fine. If the head unit has no amplifier, how does amplified signal get to the speakers? Does the stock Nissan amplifier route the signal back from the amplifier through the head unit?

For the time being I just want to listen to the 4 speakers in the doors. Has anyone installed the "Premium audio" into a base vehicle? I can find absolutely NO information that is helpful. I have asked in numerous Nissan forums with no success. Thanks for reading!