What I meant was create your SP to expect 6 parameters and pass the six parameters to it during the call.
...and call it with somethng like...
CREATE PROCEDURE proc_MLS
-- return result
One thing to note that I just thought of is that you are assigning values to the var @listingnumber as you are passing it to the SP. I think this will not work. You need to assign the values to vars then pass them in order as my example.
SQL = "EXEC proc_MLS('" & MLS & "','" & MLS2 & "','" & MLS3 & "','" & MLS4 & "','" & MLS5 & "','" & MLS6 & "')"
set rsListings = oCon.execute(SQL)