Cool. I'll try to play around with HU crossover off.
By the way, I'm using the stock rear speakers as filler only, will it be better to cross at 200Hz -12dB/oct so it doesn't go into deep bass (thus not disturbing the sound stage)?

They are still handy when watching DVD or video (my HU can playback DVD and video, although small 7" screen ) so I just leave them there.

You can play with equalizer to flatten the frequency response or to you liking.

First time I heard this kind of problem, cutting off on braking. Seems to me like the sub is cutting off on low amplifier headroom power. I guess the feature to prevent voltage drop in car electrical system. Possible cause that I can think of:

1) Alternator is not providing enough power, but I think less likely with modern alternator. It is either work or dead biggrin.gif .
2) The wire to sub is not thick enough to provide enough current to the sub-woofer or the ground contact has high resistance. When tie the ground to the body, the body paint insulate the contact and contact probably just through screw threads. Not good enough I guess.

The wire used to connect the subwoofer comes together with the original box so I doubt Pioneer is giving underspec wire. I now suspect it's either connection problem or not properly grounded.

I don't have an amp installed and the subwoofer is directly tap to the battery terminal.

My subwoofer specs:
Maximum input power: 150W.
Nominal input power: 50W.
Frequency response: 40 - 200 Hz.
Sensitivity (1W/1m): 101 dB.
Woofer size: 21 x 13 cm.
Woofer material: Aluminium cone woofer.
Voice coil type: Heat-resistant 4-layer dual voice coil.
Built-in variable LPF (50-125 Hz, -12dB/oct): Yes.

Currently I've settled for this setting:
Time Alignment on, listening position 'Front Right'
Front - HU HPF on, xover at 80Hz, -12dB/oct
Rear - HU HPF on, xover at 125Hz, -12dB/Oct
Subwoofer - HU LPF off, using built-in passive xover at ~80Hz (analog turning knob  ), -12dB/oct
Equalizer set to flat, all audio enhancement effect like bass boost, auto leveling, etc. are off
90% of my music sound nice with this setting.

Just one problem, the FM radio streaming quality is pretty low so whenever I switch to FM radio my ears suffer.
I wonder if there's any method to improve FM radio audio quality?