I have the Alpine sub in the back, not sure if that means it has the full Alpine system or not but I would assume it does.
The previous owner swapped the stock head unit out for a factory 430 unit which works just as it should. I was planning on replacing the speakers and other stuff to try and get better sound out of it. Before I do that, is there anything he could have done during the HU swap that would affect the audio performance like bypassing an amp or something? Is that HU just not compatible with the Alpine system?

2014 4 door

Thanks