Haha...no, seriously, the most classic example of a stacked instrument would be to break down something, say an orchestral percussion section, drumkit, etc., into individual components. Say different snares, which are all mapped to the same key range, different crash cymbals on a different keyrange, etc.
Then you'd call a complete set with a GSI file, which would load the stack onto a given channel. If you wanted to switch out components, but keep everything mapped the same, you'd just switch out the single GIG file within the stack, and save the whole thing as a GSI file. If you embed your GigaPulse components in a "dummy carrier" GIG file as well, you can call up (and exchange) those, too, as part of the GSI spec.
This is different than using the old GSP spec. GSP resets the entire GigaStudio environment. GSI affects only the channel you drag it onto. So, where instruments like the White Grand, for instance, used to use a GSP file to load several disparate components--now one can do this with a GSI file without resetting the whole environment.
Hope that helps clarify it.
Also, stacks are handy for live playing. You can load up a lot more than your controller can conveniently "control" and mute/unmute to access different instruments.
A cool thing to stack is the VGS staccatos and mod-wheel sustains for the strings. The sustain has too slow an attack for melodies. The staccato is too short for slow melodies. Together they get the job done. Play softly to decrease the attack of the staccato, use the mod-wheel for the sustain volume. Set the nominal volumes in the MIDI mixer and forget about it. It's simple and very playable.
There are many negative postings on this forum now. I had serious problems with GS3 Orchestra, blue screens and all. While I did not get help from Tascam, I did get help by reading this forum and solved the problem.
Jon asks me if I like VGS. Without his posting here I would not have voiced an opinion on the Vienna strings, because I did not want to add to the negativums.
Instead of answering Jon's question, I followed his posting on stacking instruments.
My God! You are a magician Jon. I did not like the strings because of the slow attack, which made a melody sound like wow-wow, driving me crazy (and loading an old SF2-based legato string in desperation). Now, I have so much control, I would have never found this out without your posting.
Thanks a lot. Now I love the violins! I do enjoy now GS3 even more.
Maybe a simple way to use stacked instruments, something that I do to simply layer sounds, is to stack & balance several components of what will be some thick pad thing onto one MIDI channel. This is great for textural stuff and is a big GS3 feature for me doing that kind of sound layering since most sequencers I know of won't send MIDI to multiple destinations from one track.
In the old days we used to physically route MIDI cables to multiple synths, using splitters & through ports to layer sounds. Remember those pix of rooms of DX-7s? This is so much easier now.