Assign sound fonts for each instrument?

I would like to know how to assign sound fonts for each instrument
For example, I use Salamander piano sound font, but everytime I import piano music, other weird instruments like flute is imported, instead of piano sound font. Is there any option to set this?
This is really annoying me because when I download mcsz files for orchestral pieces, the instruments set do not match, and I have to set them manually in the mixer.