Is this then a Finale problem or a Garritan problem?

Are you using the same Violin patch for both players or different patches?

I is violin 1 solo KS 1, 2 is violin 2 solo KS

Take a look at the file and see what you think. Happy to mention it to the Garritan folks as well.

A lot of the issue is not Garritan. It has a lot to do with how human playback is set up. However, just for kick, I placed a pizzicato in one of the violins at measure 83. When it plays back (HP on, GPO5-solo violin 1 KS) the pizzicato is oddly loud and the other strings are very muted. I can't find any way to fix that other than to change to the included Garritan sounds (violin solo 1 KS), but that messes up other things in the balance etc. Bottom line-playback is far from optimal in Finale, and this is taking away time from actually writing music to futz with playback issues. I realize Finale is ultimately a notation program. But given how much focus the program has on playback, along with incorporation with the (additionally purchased) GPO samples, it should at least be reasonably straightforward to use. 

The simple fact is that Violin Solo 2 KS is softer/less resonant than Violin Solo 1 KS, and even more so in the GIfF than in the GPO5 or GPO4.

Try it with both as violin solo 1 ks. Same thing happens if you add a pizzicato; the other instruments are markedly quieter and the pizz is loud. 

Are you marking one part Solo but not the others? HP quiets non-solo parts when one is marked solo.

I have no markings whatsoever. Each instrument is a solo in the Aria player. 

With these settings, at least much of the balance is improved, but if I change the notes in measure 83, violin 1 to pizz, it nearly mutes the other strings. Nothing odd about the pizz marking. 

Here is the file: I've added the pizz marking to measure 83 so go there and it should be obvious what I'm talking about. Thanks for your patience.