It's in the cargo area, but it's not fixed.
The amp is under the passenger seat, totally hidden.

I also changed my halogen lamps to HID
Both lowbeam and fog lights

 

after hours of tuning my Equalizer ( 2013 RX 350 with Navigation)
i find THIS setting the closest to my House Audio set up.
i used a trusted CD that i can play inside the house, using a BOSE noise canceling headphone, a Professional studio recording headphone and then the RX Non- ML system with aftermarket subwoofer and amp.

Volume 30
ASL - OFF
Surround- OFF
Treble 0
Mid 0
Bass 0

This, for me is the closest to natural.. again, listening to music is very subjective.
i know friends whose Bass are +4/+5 while the Mids and Treble are on the (-) mark

 

My 2010 RX350 has Mark Levinson Premium audio system. Compared to the audio in my other car, this premium audio is not of high quality. I believe the difference is the subwoofer and its amplifier. The sufficient subwoofer output really makes big difference. Although the sound quality is kind of subjective, I think anybody can tell the sound quality difference between AM radio and FM radio, and the difference between FM radio and live theater performance.

 

-bumping an old thread here-

What is the make/product of these RX stereo systems? The 9-speaker and 12-speaker?

I noticed an amp near the spare tire, but did not investigate.

I believe Lexus has used Pioneer in the past, is that true for a 2012 RX350 and other 3RX years?