Just wondering if anybody with the top of the line OEM Infinity system has done any minor upgrades, like maybe just replacing the factory door (front and back) and dash speakers, and maybe an upgraded amp? I'd really like to keep the factory head unit (and retain my steering wheel controls). I've heard some people talk about 5 channel amps that will support a future sub woofer placement, if I can ever decide which space in the cab I want to give up (i. e, armrest, under fold-flat in the rear, etc. ) Also wondering if anyone has done just the speakers with good results, or if the factory amp is just too weak. Don't want to spend a fortune and I'm not a kid anymore so I don't need window rattling bass waking up the neighbors as I come and go. Crutchfield says the '04. 5's have 6x9's up front and 6. 5's in the back doors- does that sound right? Any ideas/suggestions would be much appreciated!