I just bought a 2008 HHR in excellent condition. It's had one owner & the radio & speakers are all original. I know NOTHING about updating the sound and was hoping for suggestions from someone who's already vetted the options.

 

Log into crutchfield’s and select one of the many HU’s , speakers, adapters and wiring interfaces.

 

Dont buy anything Sony. I've had terrible luck with them. Bought 3 different units. The rear speakers volume is low on every one, The fader adjustment put full rear has a muddy sound distorted sound with newer JBL speakers. On the unit in my 79 Trans Am, it just didnt sound good and could not get it to sound right. I have high end brand new Polk audio speakers in that car. I dumped that stereo and put a Pioneer in it, much better.