soundfont mapping

Hi, I'm trying to create a soundfont that I'd like to use in musescore, however I don't understand how musescore chooses which instrument in the soundfont to associate to a certain part. Say I have a a caixa and a surdo (both brasilian percussions) instrument in the soundfont - how do I get a certain part in the score to use these sounds?

full story:
I'm on Archlinux, using musescore 1.1. I've created a simple as dirt soundfont in swami; first thing I've tested the soundfont with qsynth and it works as expected. qsynth lets me associate an instrument from the soundfont to a midi channel - when it recieves midi on that channel it plays that instrument.

In musescore I create a new score with a random instrument (say Violin), then load the soundfont in Display -> Synthesizer. Then I enter some notes in the Violin part, but I get no sound when I hit play (BTW sound works ok with a GM soundfont). The notes entered are in the correct midi range for the soundfont - to check I enabled Jack midi output in musescore and looked at what midi it was sending while playing the violin part.

I tried opening the "Staff Properties..." and changing the long instrument name from "Violin" to "baba" - that's exactly how I called both the "instrument" and the "melodic preset" in swami, but still I get no sound.

any kind of help is much appreciated!!

renato