Some Questions about Non-Bose Volt Audio Improvements

I have a 2014 Volt, I've had it for a few months now. I bought it to replace my 2010 HHR that got totaled. So far I really like the volt, but I feel like the audio is severely lacking. I have a base model volt, and I plan to make some changes to the audio system to improve it, as limited as the ability to do so is. There really isn't much information available about the base model Volt's audio system here, it seems that most people on here have Premium Volts. I know I can't replace the receiver, as it is part of the CAN, but I can at least replace the paper speakers with something more substantial, and I would like to add a low power amp and sub to give the audio more range. As I understand it, the Bose system used in the premium Volt is run through an amp that is rated for ~ 150 watts, with that in mind it is probably safe to say that a 200 watts class D isn't asking too much from the volt, please correct me if I am wrong. My big concern is the audio output from the receiver, and into the amp. I'm used using the low level outputs from after market receivers, and I'm not sure how to proceed with adding an amp to a system that does not have low level outputs. Does anyone have any advice or recommendations on how to do this?