[MJ777LR]

Hi all, I finally got down to installing a set of Jehnert Flatlines powered by an XD600/6. My setup is as follows:

Ch 1 & 2 --> Jehnert Midrange/Tweeter Crossover --> Mids/Tweeters in doors
Ch 3 & 4 --> OEM Rear Speakers
Ch 5 & 6 --> Jehnert Midbass Crossover --> Underseats

I have the XD600 set to 4 channel mode, so it's summing the inputs for Channels 5 and 6. The questions I still have on my mind are:

1) Since I am using the Flatline crossovers, do I still need to set Ch 1 & 2 to high pass and Ch 5 & 6 to low pass? Or should I leave the filter mode to 'off' on the XD600? Ch 3 & 4 is set to high pass since it's powering the OEM rears.
2) If I should still use the lowpass/highpass switches on the amp itself, what are the recommended crossover frequencies for the Flatlines?
3) What gain settings are recommended for the Flatline midrange/tweeter and the underseats when hooked up to an XD600/6?

Here's where I am having some slight issues.

I have the gain for Ch 1 & 2 set to the minimum level, as setting it to anything higher and I seem to get some 'white noise' coming through the fronts. It's not obvious when music is playing, but when the music fades away or when I have soft music playing, I can faintly hear it. This noise was actually also present with the OEM Hifi system, so I'm not too bothered by it. I'm just wondering if others are experiencing the same thing.

Another issue I might be having is that I don't seem to be getting much bass. The mids and highs sound incredible, so far. But the lows seem a little weak. I have no basis for reference, so maybe it's doing what it's supposed to be doing. But at the moment, I don't notice much of an improvement in the lows from the OEM Hifi system (Do note I was never seeking after or expecting 'window-rattling' bass). I don't think I connected the polarity of the woofers wrongly. For Ch 5 & 6, I have the gain set to just very slightly above minimum, probably about 1/8th of a turn. I'm afraid to turn it up higher as my driver's underseat seems to be making some rattling noises on even moderately bassy tracks at moderate volumes, like as if it's being stressed too much.

Oh, I should mention also that I laid out new wiring through the car, from the amp to each of the speakers. I actually fed two sets of 16ga wire through the doors, which wasn't a completely easy task, but also wasn't as hard as I thought it was going to be!

Anyhow, could you guys give me some help with the above?