Take a look at Hualingan or Dynavin. There is a Hualingan dealer that hangs around our forum. Search for Hualingan. You can also search for Dynavin on this forum. However you will find much more information about it on e46fanatics.com. After comparing the two it is usally easy to decide which one to get. The Hualingan has a 7" screen but requires you to cut out your radio bracket (assuming you have the MID). The Dynavin has a smaller 6.2" screen but does not require any special modes to your dash.

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[Sold] 2004 X5 4.4i - Sterling Gray - Truffle Brown, Sport, Preminum, Rear Climate, DSP, Sirius, PDC, 132's (19 inch wheel), Comfort Seats
Dynavin, JL Audio Stealthbox, Alpine PDX-5 Amp