I don't know anything about the Harmony remote, but 38kHz & 40kHz are the most popular
carriers.

If you want to try HSEROUT to send data modulated at 40kHz, I just posted an example in
this thread http://www.picbasic.co.uk/forum/showthread.php?t=12628 showing how to do
it with the new PIC16F1827 using the built-in Data Signal Modulator.