Yeah Lexus for sure won't do it, you'd have to go aftermarket.
The JL Audio FiX 86 is just one of the options out there. The FiX 86 will take the signal being sent out from the factory amp and give you tuning control to fix any factory EQ to get a perfectly flat signal that you can send to an aftermarket amp. I've never used the FiX, but I have used many JL products in the past and have been happy.

There are a few other items that do the same thing. I've always like Audison products, but they're a bit more expensive. I used the Audison BitOne in my cars for years. It does the same thing, but better. You can connect speaker inputs and tune with the built-in DSP. Mosconi also makes several high end DSPs made for OEM system integration. All of these options will require a new amp though! But that is where you'll be able to adjust just how much sound you're getting from the back of the car. I'm not sure the stock speakers will handle a ton of power, though, so you could end up with new speakers as well.

Car audio is a rabbit hole you might not want to go down lol DSP, amp, speakers... there is always something else to upgrade lol

Well this is disappointing reading about the quality of the ML and stock pioneer system. I'll have to try it myself in the es and see how bad it is! I guess for audio quality and reliability I'll have to fall back on my decision and go Acura RLX. The 2019 es 350 ultra luxury has an msrp $49,425 with gps, non ML. The 2018 Acura RL msrp is $55,895 with the els system. I'm sure i could get them to match the lexus price. For the AWD hybrid package which is 7k more you get whats below:
MECHANICAL

• Sport Hybrid System
• 7-Speed DCT

INTERIOR

• KrellŪ Premium Audio System with 14 Speakers
• Head-Up Display
• Heated & Ventilated Front Seats
• Heated Outboard Rear Seats
• Heated Steering Wheel
• Power Rear Sunshade
• Manual Rear Door Side Sunshades

EXTERIOR

• LED Fog lights
• Auto-Dimming, Power-Folding Side Mirrors
• Remote Engine Start with Vehicle Feedback
• Front windshield de-icer

SAFETY & DRIVER ASSISTANCE

• Surround-View Camera System
• Front & Rear Parking Sensors

I'm interested that the RLX has rear acoustic glass, which the es does not. Seems like the big name luxury cars but acoustic glass in the rear besides the LS 500 for some reason. Genesis G90, Kia K900, volvo s90, Lincoln continental.

My current car has been sound deadened completely and has a Dynaudio esotar 2 built system which i'd bet is better than all these cars to an extent. But for reliability my only option is Acura. Volvo uses Bowers and wilkins, lincoln uses Revel, and kia/ genesis use the lexicon( rebranded harmon kardon) system.

Before you plunk your money down on the RLX I would check the JD Power ratings for Acura. They're far below that of Lexus. For me, there are many other considerations more important than a concert hall sound...

My buddy just dumped a one year old TLX. In the shop constantly.

Don't let some of the stereo negativity ruin the car for you. There are many of us who LOVE the ML stereo, myself included. You also have to remember most people go online to complain about something, a much smaller percentage go online to say everything is great. Go drive the ES 350, take a USB drive with some music, and listen to the stereo yourself! Don't let complaints on the internet from people who honestly didn't know what they were buying be your deciding factor on a Lexus.

As far as Acura, we had a 2015 MDX with the ELS system. I absolutely HATED it. Sounded like the chipmunks singing non-stop. No lows, no mids, just a bunch of higher pitched crap.
Then the car spent several weeks in the shop with damn near every electrical part related to the nagivation/sound system replaced. The dealership couldn't track down the problem and Acura had approve the repairs in stages try to find what was wrong with the vehicle.

Once they got it fixed, we bought the 2016 RX I do miss the SH-AWD system though. That MDX handled nicely.

Well I guess it would need to be an immediate gut of the car interior and deaden the es350 and install new speakers and amp. Have to run a converter such as a JL fix 88 on the stock headunit. Not something I would be fond of for paying $50k+ on a new car.

Why are you talking about sound deadening on a car that is nearly dead silent already? The car doesn't need any more deadening. It also doesn't need to be gutted... most of the complaints in this thread are people not happy with sound from the REAR DOORS in a car purposely designed to have an audiophile FRONT sound stage.

Why don't you just buy a Chevvy Cruz then, save all that money from buying a Lexus, and do your changeover. Think of all the money you'll have for the audio redo. Probably need twice as much sound insulation but what the hey. When finished you'll have a real gem with an audio system everyone will envy...

I think the Cruze has been discontinued but he can try a Yaris.

I've already gone down that route with my current Toyota. Applied aluminum tiles around the chassis for vibration control, mass loaded vinyl everywhere with melamine foam sheets on top. That is why I want a car with a quieter engine and acoustic glass everywhere and better suspension. I could probably get the same ride or better if I did aftermarket air suspension and dropped my wheel size to 16's. I can't increase my window thickness like a true luxury car lol I had my eyes set on an 04-06 LS 430 UL since it had dual pane windows, then I had my eyes set on a 2015 kia k900 which was identical to the lexus and not ancient. The biggest plus was no air suspension! Reclining rear seat, full acoustic glass, V-8, soft close doors, lexicon system. It's a true bargain, but i was afraid of reliability with only 500 sold per year. The biggest mistake is to buy a car with air suspension or active variable suspension.

Which vehicles have acoustic glass on all windows? I thought it was just the windshield and front windows. You mentioned the K900, but they just have the front area acoustic, the same as my '13 ES.

"An acoustic film on the windshield and front side glass dramatically quiets the cabin as does the use of resonance chambered wheels, which reduce road noise while driving."

https://www.kiamedia.com/us/en/media...design-for-kia

I tend to agree on the suspension concerns and I actually opted for an ES Fsport without that option intentionally. As far as Kia is concerned, I wouldnt worry much about reliability. My experience with Hyundai products is they are pretty durable.

The previous model kia k900 v8 luxury has rear laminated glass.

Interesting video, but I still can't find any supporting documentation claiming any year K900 has rear acoustic glass.

Edit: I searched "Laminated" and found it was available on the 2015, at least. I wonder why they got rid of it if it was that noticeable.

I checked with my local audio store who does have the equipment you mentioned. After some research, they said there was nothing they could do. The speakers in the rear are too small and installing a larger amp would just blow them out. I know they wanted to find a solution but said they just could not recommend anything. Suggested I just learn to live with it. Wish I had a different outcome.

I think we are all going to have to wait for a fix from Lexus if they ever decide to develop one.