Installing Amp in 2013 Passat with Factory Fender Amplifier

So I would need a processor to take one input from let's say left rear bass speaker and then the other input to be the subwoofer?

Would an lc2i be a good choice? I still don't know how to give it back the filtered out signal though if I'm understanding right

If you have a summed output, that'll go to your amp, then you use the crossover built into the amp. I should also mention I've never used one of these before either, so I can only speak in generalities.My ex once told me I have a perfect face for radio.

Thanks @geepherder for the help. After doing a bit of reading it seems that the LC2i will be a good choice so I ordered one on sale on amazon. Now the question is just what wires to use to feed its inputs. I posted a request in the wiring diagram section asking if anyone has one for my car to help me figure it out. I just need something that will at least give it the full bass spectrum which Im convinced the sub outputs Im currently using do not provide, Im sure they are filtered extra low.

I would use 2 PAC sni-35 and 2 y adapters to build your own summing module. Connect 1 SNI to the sub wires that you are already connected to, connect the other to the ones you are calling bass speakers. Using the 2 Y adapters connect the 2 lefts together and run to amplifier. Connect the 2 rights together and run that to amp as well. Use the gain controls on the SNIs to achieve your desired sub to mid bass level.

Radio 12V      Red/Yellow      +      Radio, 16 pin plug, pins 15, 16            Radio Ground      Brown      -      Radio, 16 pin plug, pin 12            Radio Ignition      (Infotainment CAN)                      Radio Illumination      (Infotainment CAN)                      Factory Amp Turn-on      (Infotainment CAN)                      Left Front Speaker (+/-)      Brown/Green - Brown/Blue or Green - Brown      +,-      Radio, 8 pin plug, pins 3 - 7            Right Front Speaker (+/-)      Brown/Red - Brown/Black or Blue - Brown      +,-      Radio, 8 pin plug, pins 2 - 6            Left Rear Speaker (+/-)      Red/White - Brown/White or White - Brown      +,-      Radio, 8 pin plug, pins 4 - 8            Right Rear Speaker (+/-)      Red/Violet - Brown/Violet or Yellow - Brown      +,-      Radio, 8 pin plug, pins 1 - 5            Left Front Speaker - With Amp      Brown/Green - Brown/Blue (woofer); Blue/Black - White/Black (midrange)      +,-      Amplifier under driver seat, 38 pin plug, pins 18 - 6 (woofer); pins 13 - 14 (midrange)            Right Front Speaker - With Amp      Brown/Red - Brown/Black (woofer); Red/Gray - Brown/Gray (midrange)      +,-      Amplifier under driver seat, 38 pin plug, pins 15 - 3 (woofer); pins 12 - 11 (midrange)            Left Front Tweeter - With Amp      White - White/Black      +,-      Amplifier under driver seat, 38 pin plug, pins 8 - 20            Right Front Tweeter - With Amp      Gray - Gray/Black      +,-      Amplifier under driver seat, 38 pin plug, pins 19 - 7            Left Rear Speaker - With Amp      Red/White - Brown/White      +,-      Amplifier under driver seat, 38 pin plug, pins 9 - 21            Right Rear Speaker - With Amp      Red/Violet - Brown/Violet      +,-      Amplifier under driver seat, 38 pin plug, pins 22 - 10            Subwoofer - With Amp      White/Red - Brown/Red (coil 1); Gray/Red - Gray/Brown (coil 2)      +,-      Amplifier under driver seat, 38 pin plug, pins 16 - 4 (coil 1); pins 5 - 17 (coil 2)            Aux. Audio Input Left (+/-)      Yellow - Green      +,-      Radio, 12 pin plug, pins 1 - 2            Aux. Audio Input Right (+/-)      Gray - Green      +,-      Radio, 12 pin plug, pins 7 -

@i am an idiot, wow, thank you so much for the wiring, that is amazing and also thank you for the advice. Even though I have bought the LC2i, Im not dead set on the idea of using it so in your opinion its going to be better to use what I have installed already and just add the second set and Ys then vs using 1 bass speaker and 1 sub speaker wire and use the LC2i?

Or use the 1 you already have and put the lc2 on the bass speakers. Y adapter from both the lefts, old loc and lc2, rights together to right input of amplifier. Use the gains on lc2 to adjust sub to mid bass levels. If the original loc has gains that would be great as well.

Ok I think I understand that and I should have all the right parts coming to do it either way. One thing I discovered while trying to properly set my gain tonight was that my factory radio/amplifier does not have any bass roll off because I could crank it to 90 percent volume and the bass kept increasing with the volume at least to the untrained ear. Just an interesting tidbit. Anywho, hopefully in the next couple days I can get this installed and update the thread and let you guys know how it worked out.

Well today I fought the Vegas heat of 109 and chose to try the cheaper of the two routes first with the LC2i on hand just in case. I got another LOC hooked to the rear speakers off the factory amplifier hooked to my amplifier via Y cables and I feel like I picked up more range and could now utilize my LPF on the amp more to control sound. So now I hear it hitting more in rock music than it did before for sure but it is comparatively weaker than lower notes. I know normally these could be apples to oranges comparisons but in another vehicle I just sold I remember some of these songs hitting equally hard. I'm starting to wonder, could this be my amp now that I have hopefully solved the range input issue? I have never used kicker brand before and never such a lightweight amp for 2 ohm, I bought it with the intention to go 1 ohm. With only 6db bass adjustment am I damned from the start? I dunno where to head at this point because I'm dealing with two variables I have never worked with, factory stereo/amplifier and a underpowered amp.