I was thinking to upgrade my subwoofer since I upgraded the all oem door speakers with infinity last year. I bought infinity from sonic electronics ca with amp kits PK8Z ( which you need ). It comes with db Link 8 Gauge Power Series Amplifier Wiring Kit with AGU Fuse Holder. You donot need the line level out adapter. The basslink has built in line level. I disconnect my oem subwoofer connection under the passenger seat. I connect the rear doors speakers with the new amp and it sound great for a vehicle. All you have to do is running the power from the battery to the new amp. I read johnystan diy in the forum for routing the wire from the battery to the back of the left side of trunk. I connected the ground at left side of vehicle ground location behind the rear seat left side. For the infinity basslink volume control wire routed by door sills to the front dash near the gear shifter. I attached the amp at the left side of the trunk seat in a piece of wood holding by two screws by cargo liner hook. It is easy to remove for access the spare tire. Here is some pics.

 

Wire from the battery run at the driver side fender cover. Here is the link:https://www.clublexus.com/forums/rx-...tall-pics.html
More pics.

 

Did u keep the stock stereo

 

Yes. But I replaced all door speakers with infnity and disconnect the oem sub woofer.