Reddit mentions of SCOSCHE SLC4 Car Stereo Speaker 4-Channel Audio Lineout Converter/OEM Amplifier Adapter with Adjustable Level Control's

We should see how the radio was connected to the amp, the problems with the Bose amps arise when connected though the RCAs of the HU, it seems counterintuitive but you get better sound using the speaker outs since they are balanced and the amp inputs too, you can use a level converter designed for Bose if the signal is too high.

It's a Sony XAV-AX100 You'll need this Metra Kit to fit the new stereo. If you have a Bose system you'll either need to bypass the Amp or get a line level converter. I started with the line level converter, the sound is better than the stock system but still not great. I plan on getting a new amp and speakers eventually. I just wanted bluetooth and Android Auto to start.

Thanks but I don't want to splice the factory harness.

I am gearing towards using an adapter and a LOC to do the job.
Could you confirm if I can use the Metra 70-8112 harness and the Scosche SLC4 Line output converter to get the job done? I think this is going to work but I'll be using the factory amp.

This is what the youtube video was about.

You could always get a 4 channel line output converter to convert speaker wire to rca. But a HU with 6+ rca outputs would be in your favor. Sub out, Rear out, Front out

https://www.amazon.com/SLC4-4-Channel-Converter-Amplifier-Adjustable/dp/B000BFL52Q/ref=sr_1_3?keywords=4+channel+line+output+converter&qid=1573677351&sr=8-3

https://www.amazon.com/Pioneer-DEH-S5000BT-Compatibility-Bluetooth-Customization/dp/B07526JF15/ref=sxin_2_ac_d_pm?ac_md=4-2-QmV0d2VlbiAkNTAgYW5kICQyMDA%3D-ac_d_pm&keywords=car%2Bstereo&pd_rd_i=B07526JF15&pd_rd_r=2b2e20e3-4a81-430a-9209-334d8955226f&pd_rd_w=b6SGp&pd_rd_wg=m4dWc&pf_rd_p=02e79b16-eab7-4369-852f-d04a58a4d9b5&pf_rd_r=YG038249XGV2DVT292CQ&qid=1573677664&th=1

Most likely your HU has all audio being output through one set of rca's. Or sub only. But if it has been playing it's all audio, just needs a signal split. That's where a 4ch converter comes in handy.

As for grounding the rca's, you shouldn't have to, but I learned the hard way that they can be grounded manually by using a piece of speaker wire attaching ONLY the outer metal of the rca (not the center prong) to the stereo chassis (metal on the stereo). Here's a shitty video I found on youtube that can help.

https://youtu.be/O6B8fJ_RxFU

All in all, upgrading HU with more outputs would be your best choice

Ok, what I'm thinking now is a system that looks like this: http://imgur.com/nQEW57b

Would this work? Would it output strangely because the soundbar wants to have a left and right side, so it would be a bad center? I'd really like to use it because I think it sounds pretty good and I already paid for it.. you know. In hindsight maybe I shouldn't have, but too late now.

The speaker to line converter I was looking at was this:
http://www.amazon.com/Scosche-SLC4-Speaker-Level-Converter/dp/B000BFL52Q

I know its made for auto use, but it shouldn't matter. It will handle 80W, which is the maximum output of the receiver I was looking at:
http://www.amazon.com/Onkyo-TX-NR515-7-2-Channel-Network-Receiver/dp/B0077V88VI

I can get that for $100 less refurbed on ebay. Not too expensive and it will allow me room to expand my system as I save up a bit, assuming everything I have come up with here works. I'm having a bit of a hard time finding a receiver with zone 2 being preamps, they seem to all be powered.

Edit: Other solution would be to run the soundbar as L+R and turn the center off I guess. Are there any issues I should be aware of with using the speaker to line converter? I also have input options of Optical Audio and HDMI if those would be potentially easier to convert to.