I do not have much remaining hair that can be pulled out, so I hope someone can help me out.
I have Finale 2006c and use both full GPO and JABB. I also use HP. My problem is that I cannot access the various brass mutes in the JABB library. Though I do have a keyboard, I barely know how to use it, and do my score entry using a combination of Speedy and Simply entry.
I don't own JABB, Ron, but I suppose the mutes are part of KS instruments, yes? In that case you should be able to create your own KS expressions using the "Dump" playback option.
In this example, "$05" is the GPO "9. Notation" pizz KS: it is MIDI note #5 ("$" means the number is hexadecimal, if you enter a number without "$" it will be interpreted as decimal) - middle C is MIDI note #60 (decimal) for reference. You can leave the other numbers as they are in the example.