Yes the magnets are very strong. So much that if it was magnet to bare metal you woudl have to pry it apart with a screw driver. But with the magnet behind the felt, it holds just right.
I ended up getting the same one. I have this dual female 12v adaptor wired into my +12v ignition on, so when the car is trunned on power is sent to the Nexus 7, the blue tooth adaptor and the Wi-Fi hot spot. All 3 are 12v to usb.
Do you NEED the x-over? The Bose symphony II amp should be enough?