I have the standard audio system which really sucks in my opinion. I want to upgrade but will take things one step at a time, the first being new speakers. I found some information that the stock amp impedance is 4 ohm. Can anyone confirm that? And what have folks done about a sub? I don't want massive thump or a box that takes up space in the back - I just want solid bass that is not likely to come from the 6.5 inch door speakers. I am an old fart, so no head banging, hip-hop or electronica. Thanks