Sounds like the problem may be a bit of physics.
Considering the cabinet is sitting in the trunk of your 2004 Maxima and the ports may not be placed ideally away from a solid surface to allow pressure, combined with the "sealed" trunk, it stands to reason that your results would suffer.
I suggest folding down the rear seat (if possible) and try to place the cabinet so that the port is about 8 inches from a "wall".
Check your phasing .