GSX can be used with any airplane. It supports internally all default airplanes and many popular 3rd party addons, this is the updated list:
http://www.fsdreamteam.com/forum/index.php/topic,5481.0.htmlBut if the airplane you use is not supported internally, you can create a configuration for it, using the integrated airplane configuration utility included with GSX.
And of course, GSX is sold in Try before buy, and the free version works in full at 3 default airports and all FSDT/Flightbeam airports too, so you can install it and test it without limitations at those airports. Purchasing GSX will allow you to use it everywhere.