To import all channels of an OpenEXR file, do the following:
Once you have selected “all channels,” a new node will appear in the Schematic, which displays tabs that each correspond to an output connection. In other words, all channels are imported into different import nodes which creates a group with multiple output connections that corresponds to each import node’s output. The following image displays a UI with two schematics. The Schematic on the left displays the group node, the Schematic on the right displays the import nodes with their output connections.