I'm using Directory Opus v9.5.4.0.3806 x86. I wan't to create a short-key (eg Shift-Enter) for opening a directory or an archive file which is selected in one pane, in the opposite pane just like in Xplorer2.
Set Hotkey as desired (to set Shift+Enter, hold the shift-key and click the drop-down arrow to select Enter)
For function, enter Go FROMSEL OPENINDUAL
Click OK, then OK
Note that by default Shift+Enter is already defined, so you'll need to delete the existing one first (also through the Customize/Keys dialog) if that's the key you want to use.