The IR blaster port on the cable box is purely output.
There are some settings that may help, though -- on the replay, go to the input setup, on the screen with the list of IR codes. Scroll to the one that works the best, and instead of hitting select, hit the ZONE button -- that'll take you to a fine tuning screen, where you can modify some settings, including (depending on the code) whether or not to send ENTER, the number of digits to send, and how long to wait between each digit and between separate commands.
There are some settings that may help, though -- on the replay, go to the input setup, on the screen with the list of IR codes. Scroll to the one that works the best, and instead of hitting select, hit the ZONE button -- that'll take you to a fine tuning screen, where you can modify some settings, including (depending on the code) whether or not to send ENTER, the number of digits to send, and how long to wait between each digit and between separate commands.