Installed my New Alpine PDX-M6 with one Alpine SWR-12D4!!!
Amp was rated at 658 RMS so using a Multimeter I tuned the amp to push 37volts at about 3/4 volume.
This thing rocks!! Not overly boomy and the SQ is simple amazing. Such a great addition to the Premium audio system.
Loss very little trunk space.
Here is a installed pic
2013 X3 28i Alpine White/ Black Nevada Leather/premium pkg/convenience/sport/DHP/Cold weather 1/Premium sound/Parking sensors/Alpine PDX-M12 AMP powering one Alpine SWR 12D4