How bad/not so bad is the stock sound system?

Are you an audiophile? If yes, pretty bad

If you are not an audiophile ,not too bad especially if you mainly listen to Sirius 114

If you like vibration hertz, then stock subwoofer is very weak.

Not sure why Lexus decided not to provide ML as option in the USA on 450h+. It was a pure marketing move to sell more 350h, because ML is available on 450h+ on Canada and maybe other international countries,

I had CT200h and spent $3,000 to upgrade standard audio to sound decent. It is (possible to upgrade 450h+ to decent audio ( note: this can be done without upgrading subwoofer, but most people like subwoofer vibration }. There are several threads on this forum for very nice 450h+ audio upgrades DIY looks like quite a bit of work and still substantial expense; professional upgrade even more.

Good Luck and Good Audio

YMMV,
MidCow3

P.S. - Of my cars I have now, the 350h is not the most driven even with the ML
P.S.S. Yes, I have a "nice" subwoofer on my home system, SVS Model PB12-Plus Rosenut

I love my music. Our 24 350Lux has the ML. I do enjoy it.
I would not upgrade a car system at this time of ownership. Prefer to buy right the first time.
also when I’m with my wife I might as well listen to radio static… can’t enjoy what I like at an increased volume

haha. If you really like music buy the ML one with better clarity and more speakers. I had an order for NX350h w/o ML and the pioneer was workable but lacks bass IMO. I was thinking I could/should have thing 1 day.

I wanted to buy it right and some extras so I went to NX350h LUX with ML, triple beam led headlights, turning lights, 2 way lumbar support, etc. I hope to keep this NX for a while. I even going to add PFF onto the vehicle.

I tried the audio a number of times and came to the same conclusion on getting ML one. No idea why they didn't put ML on the NX450h model in the US.

Pioneer:
ML:

Sounds curious as to whether you have made a decision yet. Are you going to use lexus of lehigh again? Hope all is well.