Looks great so far. I just did a similar install: 750w rms NVX amp and a Sundown E-10 in a ported box. I love it! BMW makes the install pretty easy by having everything in the trunk. You can connect the power line easily where the main power line from the battery goes through the trunk floor under the car. There is a stud with a nut that can be undone so a ring terminal can be slipped over and retightened. No need to connect directly to the batter since it’s such a short run. The negative can be connected to the stud where the main negative battery cable connects to the chassis.

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2007 E70 4.8i