You can use (just about) any of the particles included with Particle Editor and you can create your own custom particles in Particle Editor, too, and use them in GameGuru MAX. Currently, the AGK version does not automatically link to MAX like the MAX version of Particle Editor (which is identical, apart from being linked directly to MAX). However, TGC has said they will supply a solution for those of us that own the AGK version so that it will be linked to MAX, too. That could be an update to our AGK version or perhaps giving us a Steam key to the MAX version or ... ??? We will just have to wait and see. One source at TGC states they hope to know more in the next day.
In the mean time, just use your version of the Particle Editor as normal. Once you have the particle you want, click the Save Icon near the top-left, give it a name, and save. The saved particle will be placed in the Particle Editor folder in media>export. There will be four files created for each particle you make ... name.arx, name_g.png, name_r.png, and name_sx.png. Copy all four files and go to the following:
Documents>GameGuruApps>GameGuruMAX>Files>particlebank>user
Paste the four files here. Then, once you are in MAX, you can access your custom-made particles by go to the Particles bar, clicking on Add New Particle, and then going to the User area in the pop-up that shows up.
Intel i9-10900K 5.10GHz, 64 GB RAM, Nvidia GTX 1080 ti 11GB, Windows 10 64-bit, dual monitor display