I'm buying a used Roland BK9. I knew that BK9 can import sample
loops thru " Audio key"function but wondering if it can also
import multisamples or not?

No, it can’t. The Key Audio thing is primarily for short loops (2-8 bars, sync may be an issue with longer loops).

I *think* the E-A7 can import multisamples. Probably the only Roland arranger that can do it. But even on that board, it only accepts a few formats and the memory is limited compared to a TOTL workstation.

I love Roland. But if you want to do a lot with samples you might be happier with a Montage, or at least a Motif XS. Yamaha has programmed "arps" which are like style tracks, in that they support a form of chord recognition. It's not exactly like arranger chord recognition, but depending on your priorities, the Montage (or Motif XF, XS, etc.) might also be an option.