2015 Prius 3, Trim 4 JBL, amp replacement

if I have the JBL amp I see pictured in the Crutchfield, does that suggest the head unit is putting out something line level? like swapping that out to put an 5 channel amp or crossover splitter for adding a sub in the trunk?

Like perhaps this could be a good way to avoid replacing the head unit?

 

I mean to say, if my car is using an external amp already because of the premium JBL sound system as it suggests on the Crutchfield site, doesn't that suggest at least that the head unit does actually have line level outs that just aren't conforming to the RCA standard?

 

Crutchfield's site is claiming I can use a Rockford Fosgate DSR1 without having to cut factory wiring... anyone tried this as an alternative to replacing the head unit?