[montr]

I am upgrading my base audio (2010 E90 335d) using the Alpine kit 65-41-2-163-268. The 268 kit does not require any wires cutting (plug-and-play) but per instructions required radio recoding. There is another Alpine kit 65-41-0-445-684. The 684 kit require wires cutting but no recoding.

I studied the instructions of both kit, wiring diagrams, parts number, etc . Here is what I found:
1) Both kit used the same amplifier.
2) Both kit end up to be connected to the car the same way. The difference is that the 268 kit use connectors and the 684 kit use crimp wires.
3) For the 684 kit, you are instructed to put the switch on the Alpine amplifier to position #2 to equalize the response (undo the equalization in the radio). For the 268 kit, you are instructed to put the switch on the Alpine amplifier to position #1 (flat?) but you have to recode the radio to remove the equalization in order to get a flat response.
4) You can convert a 268 kit to a 684 kit by simply cutting the connectors on the kit that connect to the radio and speakers.
Here is my theory. I should be able to use the 268 kit without recoding the radio by putting the switch on the Alpine amplifier to position #2 instead of position #1.

I hope to verify this soon. I ordered this week a 268 kit from Denmark Schmiedmann. In the mean time I measured the audio frequency response of my car. See attached response. To measure the response, I created a CD with a filtered flat white noise (200Hz to 20KHz). I used the sound card (16 bit @ 96KHz) of my laptop to capture the output of the radio. I did a Power Spectral Density of the data using Matlab.

Note: With Bass=0 and Treble=-4, the frequency response is within -1dB and +2dB.