In terms of factory available audio systems, the HK is one of the best I've had. I'm very pleased with it. From the "Big 3," I think it's the best out there. Some luxury car manufacturers have better, but you're talking a $6,000+ option from those high end systems. You can get better if you're an audiophile with an aftermarket system, but aftermarket systems come with their own set of issues... installers being the number 1 issue.
In the Challenger, it has more bass (larger trunk unit) than the Charger. It's a decent quality bass... loud enough to feel it and the 18 speakers are nice if you have an input that supports directional audio. Sirius/XM and the FM stereo don't use the positional audio. To really experience it, you need to plug in a bluetooth device with MP3/MP4 audio loaded up. Then, you'll hear individual sounds coming in from all over, provided the recording allows for it. I have a Prague Philharmonic album that's all movie scores... like Superman, Batman, Indiana Jones, Star Wars, Last Starfighter, etc. That album is fantastic in that you can hear the strings at the front right of the car, brass at the front left... drums at the rear and so on.