Sain James Orchestra soundfont

Only add the sf2 files you want to use in the synthesizer, then move them below the soundfonts you have loaded that include all of the instruments. Use the arrows in the synthesizer to do this.

You then need to open the mixer (F10) and assign these sounds to the instruments in your score. If you have any full sound fonts loaded, they should each begin with a Grand Piano, this should tell you when you are looking at another soundfont. When you get to the SJO sound fonts, near the bottom of the list, you will find the instruments you have loaded. Since I'm not familiar with the set up of the SJO, I'll speculate a little. If you have Clarinet, then Trombone then Violin loaded, you should have between about 1 and 6 sounds for instrument in this order (Cl, Tbn, Vln). You can assign these sounds to the instruments.

If there is an instruments.xml file included, you need to open preferences and add it's location to the score tab in Instruments list 2. This should give you a group of instruments (like Jazz, orchestra...) that somehow identifies it as SJO in the instruments dialog (press i to see it). If you see these instruments, then the assignment of the sounds should be automatic, just make sure you have the sounds you need loaded in the synthesizer.