Line Output Converter to 5 Channel Amp

You would use a four-channel LOC, tapping into the speaker wires for the signals.  Fronts go to 1 and 2, rears go to 3 and 4.  And you would use Y-splitters to share the front signal with the 5th channel sub.  Fading the head unit will then keep the fronts consistent with the sub, and the rears can be faded down by themselves without interfering with anything else.

There are several brands of high quality LOC's.  Besides the two you mentioned, there is Peripheral, David Navone Engineering, Soundgate....and others.  I recommend the NE774V.  Qualities to look for include:  adjustability of voltage, isolated internal grounding and a built-in subsonic filter.

Twisted wire is the key to success with a LOC.  The LOC should be positioned where you have easy access to it for adustment purposes, and most experts say to place it close to the amp.  The twisted speaker wire, then, is soldered into the proper OEM wires, and is run (away from power wires) back to the amp location.  Another method probably more often used is to place the LOC behind the head unit and run twisted cable RCA's to the amp.  The first method is less expensive (twisted speaker wire instead of RCA's) and allows easy access to the LOC.

Positive twisted with negative, 1.5 to 2 twists per inch, cancels interference picked up along the wire run.  That's why quality RCA cables feature "twisted pair cables".  Additional shielding is not really needed.  Any signal input wires should be twisted pair while regular speaker wires from amp to speakers do not need to be.  I even twist the leads on the LOC, too.  HERE is one example of wiring on the market that is twisted pair.  I twist my own wires using common 20 ga. Bell wire and a drill for quick work of it.

(BTW...there isn't one of us (regular contributors) on this forum who doesn't learn something new almost every day   :)

If you just want to buy some already twisted speaker wire that isnt too expensive try this: http://www.crutchfield.com/S-wqtSrsPGPlT/cgi-bin/ProdView.asp?g=50600&I=211UC14 It has "zero grip" clear insulation also which would make it easier to run the cable throughout your car. 

Have a good close look at the Audio Control LC6. It will do exactly what you need it to do + if you purchase the optional sub level control, it will then afford you much more control over your system.

www.audiocontrol.com