Thanks to Randy for teaching me how to make my own sfz files for Aria. Here is a very nice toy ukulele sampled, along with a selection of string slap sounds for strum rhythm patterns. (Sorry for the lack of knowledge of guitarist's technical terms!)
Unpack the zip file into one folder. Then left click a channel in Aria (where you load the instruments) and choose Import. Navigate to the folder where you put the unpacked zip file, and select the sfz file. Ta daaaa!
Best wishes to all my Northern Sounds/Garritan friends.