Spx is a minor mode which only takes the idea of "automatic mode switching" from Lispy and restricts it to simple wrappers around SmartParens commands. Automatic mode switching means that when the point is at parenthesis/brackets/braces, your regular keys activate commands instead of self-inserting themselves.
Enable the mode with spx-mode, place the point before the left parenthesis (or brace or bracket) of an sexp and use the action keys. Note that for the left parenthesis you have to place the point before the parenthesis, and for the right parenthesis you have to place the point after the parenthesis in order to activate the bindings.
Example 1: (the point is marked with |)
(1 2 |(3 4) 5 6)
pressing k produces
(1 2 5 6)
Example 2:
(1 2 (3 4)| 5 6)
pressing k produces
(1 2 5 6)