[morgal48]

The 6X40 Haes amp has an internal low pass filter that chops the signal around 50 Hz. If you're handy, you can open the box and eliminate that. Really handy. The info is, IIRC, on Rennlist. If you're not that handy, remove the Haes amp, buy a 5-channel amp, remove the DSP, and adjust the sound to your liking. Wiring to the amp from the cabin is routed through a bulkhead penetration near the steering column, then behind the battery to the amp and CD changer. The door subs are 5-1/4", making the combined surface area 10% greater than a 10" sub behind a seat. Wire the doors in series and you effectively have 1-ohm speakers. The shelf speakers are designed for filler. A new amp will allow that sound level to be increased.