This was certainly true for me. I have a 2013 Grand Caravan with the stock 6-speaker setup and a couple of years ago I got a good deal on a Pioneer head unit and boy did it make a difference. Between the upgrade to 22 watts rms per channel of power compared to the stock radio, and the 13 band eq, the cheap ass stock speakers sound really good now. People have got into my van and asked me when I put in a system and when I tell them everything is stock except the radio they can't believe it. I'm getting ready to upgrade everything else now, but with the exception of it lacking a little on the low end punch, the setup sounds really good just from a HU upgrade.