Don't bother with that Yamaha multisample, it's no good at all.
On this page:
http://www.dedicatedtotriton.net/downloads.htm you have a good Steinway that's about 8MB.
There are two multisamples of that steinway, two different velocities of the same sound. Assign them to program in Pa1x. I don't know if it's possible to assign both multisamples in Pa1x's sound engine, didn't actually work on Pa1x.
But if you can't, use any preset piano sound, assign just first multisample (that's Stwy G 1) and save, it should work.
You can check this topic:
http://www.korgforums.com/forum/phpBB2/ ... hp?t=27640
We elaborated on the matter of multisamples pretty much.
If Pa1x can have 2 multisamples in one program, than everything written in there relates to Pa1x too.