Can the RX350 Pure Plus be equipped with a Mark Levinson audio system?

In a few years, you can, refer to es.

The mug in that package isn't important, but I find the rear seatback adjustment quite useful. It seems like there's no aftermarket modification for it yet. [I want to be alone]

There's only the 450 and 500 to choose from. I've been using Panasonic loudspeakers for a year, and they're pretty good.

I think the built-in one is pretty good. Adding more would probably cost a lot, right?

The original car's loudspeaker is decent. I'm not sure if you have particularly high standards for audio or if it's just a psychological effect.