Ok, so at this point I have the Banjo-Kazooie sounds. I found that the loop points were not set for a lot of the sounds, so I spent several hours setting the correct loop points by editing the soundfont using Polyphone. Then I loaded up the sounds into sforzando again (unfortunately Synthfont isn't available for macs and I use Logic), and found that I somehow messed something up.
Now, when I choose a sound to play, I hear the sound I chose on loop, but every other sound that is part of the soundfont also plays. Here is what is sounds like: http://picosong.com/jFj5/
Loading up the original soundfont, before I edited it, everything is normal. The sounds play as expected, just with terrible loop points. So it's pretty clear that I somehow caused this to happen when I changed the loop points. Does anyone know how I can fix this, or where I could find out how to fix this? Thanks!
EDIT: Just tested it again by starting out with the original soundfont, and making a super minor tweak using Polyphone. Same results; everything plays when I press a key no matter which instrument I switch to. Maybe there is a setting I need to turn off in Polyphone?