I’d say both but it depends. Some of the EZmix presets do not have several FX modules in them and can be used to further color sounds that are already somewhat processed.
Other Presets will sound way over the top with some SDX Presets but it, of course, depends on which SDX Preset is loaded and which drum we’re talking about.
There’s nothing wrong with experimenting, your ears decide what works or not.
