If you do want to remove head unit or amp in the DSP system you will have to 100% start from scratch.

You will need a new head unit, amplifier, speakers with crossovers and subwoofer if you want to replace the OEM system. For the cost our Stage 1 + Subwoofer and an iPod kit or satellite radio ends up being substantially cheaper and sounds quite good. Many x5world/xoutpost members here have this setup and love it!

If you have any additional questions just let me know!

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2009 E70 X5 - Third Row - Rear DVD
Past - 04 4.4i Sport Package