stock hu and aftermarket amp/sub

I am wanting to install a mono amplifier and a single sub woofer in my 1999 Chrysler 300m using the factory head unit. The vehicle is also equipped with the Infinity II Premium factory amplified setup. I have looked into several methods and devices to complete this task. PAC carries a product called AOEM-CHR.There is also using a Line Out Converter and tapping into the rear 6x9s. As well as splicing into the Line Level rear 6x9 wires and simply splice in RCA jacks. Lastly, use the High Level Input on the amplifier. To note I do already have an adjustable Line Out Converter and the amp I plan on using does have High Level Inputs as well. So, first question is what will sound quality be like with the Line Out Converter versus using the amplifiers High level Inputs? Second question pertains to the Line Out Converter. I am only planning on running one sub woofer off of the amplifier. I have read in several places, possibly on this forum, to only tap into one rear 6x9's POS (+) and NEG (-) wires and to attach both of the LOC's (+) and (-) to the respective (+) or (-) on the 6x9's wiring. Is this correct or should I tap into both 6x9's wiring? As I already have everything I need for either High Level or use of a LOC, I am not so interested in purchasing the PAC product and do not like the idea of tapping into the Line Level with spliced RCAs (unless someone suggests doing so). So, any help is appreciated and I look forward to hearing your responses!

Bump... trying to get this done ASAP...

Tap into the rear 6x9. They have a high input to the speaker so with a LOC you should be fine.

Second question pertains to the Line Out Converter. I am only planning on running one sub woofer off of the amplifier. I have read in several places, possibly on this forum, to only tap into one rear 6x9's POS (+) and NEG (-) wires and to attach both of the LOC's (+) and (-) to the respective (+) or (-) on the 6x9's wiring. Is this correct or should I tap into both 6x9's wiring? Use both 6x9 leads or just one?

Used both 6x9s for the LOC. Easy install works well. Good use of equipment I had just laying around. Thanks for the input!