Just took possession of a brand new 2008 Kia Rondo and the audio needs some help. The head unit is the factory CD/MP3 unit with an auxilary input for an Ipod or similar external audio player. Factory speakers include 2-6.75" in both front and rear doors and a 3/4" tweeter mounted high on the front doors. I'm going to assume that there is no amplification except as provided by the HU. Adding a sub ( or subs) is probably a no go. This is a 7 passenger vehicle and needs to retain the ability to carry 7 passengers. What can I do for less than say $700-$800 to markedly improve the SQ. I don't need or want a thump mobile. Nice warm tones with enough volume to make me and the passengers smile is enough.