There are no AUX sub-configs on NEXUS and bindings are global within a config for HIP and ADS.
NEXUS is a controller intended to play console games with the added benefit of motion aim, rather than a controller intended to play PC games that have a huge number of keybinds.
There are enough buttons on NEXUS to use in place of an Xbox or PS controller, with a handful of extra buttons to bind to controller actions. Double-binding, like on APEX, is possible. But AUX configs are not. Analog triggers can be configured to perform different actions at different depths, but digital buttons (everything else) cannot.
PC games will be supported by NEXUS, but only if that game supports a controller. If you want something more complex, maybe reWASD will do the job on PC. Lithe uses NEXUS to play PC m/kb games with reWASD.