🚀 go-pugleaf

I'd appreciate some advice on setting up my new Mirage PS12-90 Subwoofer.
I'm using my Pioneer AV Receiver and a pair of KEF C95 main speakers.
The best way for me to install the subwoofer, I beleive, would be to run a
loop through my receiver's lowlevel inputs and outputs, preamp outputs of
receiver to subwoofer, subwoofer to power amp inputs of receiver. No pro-
blem so far, but the cable run is about 30 feet, and even w/ MONSTER
INTERCONNECT cables there is a hum in the main speakers which the Puioneer
tech support people say can't be eliminated because of the length of the
cable run.  Is there any way around this? Can the hum be eliminated? It
really isn't that loud, but I'd rather not have it at all.

Instead of the above setup, I'm using the second choice - using the speaker
inputs to interrupt the run from receiver to speakers.  So the run goes
speaker outputs from receiver to speaker inputs on subwoofer to speaker
inputs of main speakers.  This is ok, but have couple of other questions:
The subwoofer (powered) has a low pass filter dial to adjust: 50Hz - 150Hz.
I just can't hear the optimum setting myself. Should I just set it halfway?
The phase switch, set at 0 or 180 deg. is another aural setting I'm supposed
to make, but I can't hear the difference.  I just have leaden ears, I guess.
Should I just leave it at 0?  The I have not been able to reach the Mirage
people to ask them.

Last question.  I know I'm supposed to use 10 or 8 guage w/ a run of this
length (30 ft.), but I've been using 12 gauge lamp cord - Am I really
missing much? 
Oh, one final note - my KEF main spearkers are 4 ohm impedence.  Does this
affect my subwoofer settings?
Thanks,
Ed Dentes