In addition to the general preferences, X-Particles has several settings which are used on a project-wide basis. These can be found in Cinema's Project attributes, which you can see by pressing Ctrl-D (or Cmd-D):
For the buttons at the bottom of the interface, please see the 'Common interface elements' page.
This value affects the Collisions, Fluids and Constraints (Multiphysics). Increasing the Subframe Steps divides each frame time into subframes, and this reduces the velocity per step that each particle is moved by. In X-Particles 4, subframes are also used by most modifiers to reduce the banding effect which is sometimes seen.
If you have fast moving or complex particle motion increasing the Subframe Steps will increase the accuracy of the Fluids, Constraints and Collisions. It is advised to only increase it a small amount as it can greatly affect your particle simulation result and drastically slow down the speed of simulation.
If you experience leaks from collisions, especially from rotating/moving objects or when particles are pinched between multiple objects, then increasing the Subframe Steps will help the collision engine resolve these cases more accurately.
The second use for this setting is to reduce the banding in the particle stream caused by some modifiers. Increasing this value can eliminate banding but will slow down playback, so you should keep this setting as low as possible to avoid too much speed reduction.
You can also increase this value to increase the accuracy/stiffness of dynamics/collisions and constraints.
This is the maximum number of collisions per particle within one execution. For example, fast moving particles may hit many polygons over their movement within one frame/subframe, and this is the maximum number it is allowed to hit. It is a safety limit to avoid very fast particles colliding repeatedly and slowing down execution.
This setting is used for constraints and PBD Fluids. Increase this value to make constraints and PBD more accurate/stiffer.
This setting stops the constraints/dynamics solving early, if the execution of the constraints/dynamics doesn't change the particle's velocity or position very much (in other words, if the particles are already close to the constraints/dynamics final solution). Increasing the value will improve the accuracy of the solution but at the expense of slower playback.
Please see the Constraints object for further discussion of constraints solving in X-Particles.