Re: Active Crossover questions..
Electronic crossovers are "active". That includes the LP and HP filters in an amp. Passive means no powered devices (opamps, DSP etc), just capacitors, resistors, and inductors.
HU crossovers and amp HPF/LPF can be redundant depending on the install. There's no real advantage of either. Depending on the HU your choice of frequencies can be limited but the accuracy is probably better than a calibrated knob on an amp.
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's