I gave the same information that sschreib shared.
I let me know that I was not satisfied with the sound quality of the so call 1800-watt 21 speaker ML system in my GX550 Lux+.
I think Lexus (accessories) offers the cargo mat for the OT+ models.
The cargo mat from Weathertech (401775) fits my Gx550+ perfect with the 3rd row seats folded down
I just talked with Weathertech on the phone. Customer Service confirmed that this mat (#401775) fits the back cargo area of a 6 or 7 passenger Gx550 when the 3rd row is folded down.
They do offer a 30-day money back return if for some reason you are not happy with this mat.