Sorry to post this without full diligence on the prior posts,
Thought I will post it anyway and in parallel do my diligence.
I am reading through the manuals - they are 300 pages + !
Context:
I am thinking of getting a PA5X 76 keys, and give my PA600 (a real staple for me for many years, except for some Pitch bend issues).
Questions:
1) Is PA5X sounds/styles compatible with PA series - especially PA600? where I have a large library of assets as well as custom Python Programs.
2) Does it have On board speakers? Do you need special external speakers or any good speakers will do?
3) Does it support Custom Tuning/Scales (especially user scale like PA600)
I already noted from somewhere that User Scale is Second Class - Korg does not remember it between sessions and a few other things.
4) What is the size of the built-in/default storage? *GB?
5) I observed that it has an HDMI output. Does this project the Display to large external monitor? What is the resolution? supported.
6) Does it have a Volume BAL or equivalent -- to adjust relative balance between Main and Accompaniment?
7) Is Power Supply Built-in?

That MIDi OUT stops working (see my post in PA600 forum) has been a major annoyance
9) Is the Joystick string and durable?
I had to change Joystick on my PA600 so many times.
But it is absolutely vital for Indian Music.
10) Does it Support MPE standard? Incoming and Outgoing as a Midi Controller?
11) Are there built-ins for World/Ethnic instruments and styles, especially for Indian and Asian.
12) Is PA900/PA1000/PA4X better than 5X simply from compatibility and "proven track" record.
I know this is a lot...but appreciate your sharing your thoughts on any of these.
Hopefully this also helps others in the future.
br Sri.
P.S. Last One.
a) Has anyone purchased PA5X from overseas (non-US, non-Europe) vendors? What is your experience? I am looking at ordering from India as the prices are extremely attractive compared to here in U.S.