Lee S., I purchased GPO and JABB when the sounds were packaged with kontakt as their sampler. With the current version 3.x of kontakt you can setup multis which preloads a bit of each sample (voice) and then you can send program change numbers to switch between the various preloaded voices.
So it could be in their current Aria version you cannot do this....that is a poor design decision on their part. They will change otherwise the competion will do them in, e.g., East - West.
But how will they get their GM Wavetable to work. This will likely have something like a 1GB or 2GB of sounds preloaded into memory either entirely or in part with the rest streaming from the hard drive.
What do I know???