interesting. i bought a cheap china android head unit off amazon, i ran it for a couple weeks but didnt like it at all so i sold it and installed the oem one again. really want one with android auto so i'll keep looking for that and see how it sounds. i could be imagining things but i swear the rear oem speakers produce more bass than the new front ones right now.
Well, when I said that an aftermarket head unit would do better than the OEM head unit, I didn't mean cheap china junk. There are plenty of Kenwood, Pioneer, Alpine, and Sony head units that have Android Auto that will be leaps and bounds better than the OEM head unit.
The OEM head unit has some digital processing going on, and it's certainly possible that the processing applies a HPF to the front midbasses, and allows the rear speakers to play lower. This is a product of the processing in there stereo, not the speakers themselves necessarily.