The most reliable way we have found is to leave the IR adj as is out of the box.
Turn the RF all the way down to 0, then turn it up just a tick.
Put the ir blaster right over the ir pickup on the 8300.
keep the rfx box away from the cable box....if you see the "rf" light flicker even a little bit (while there is no remote activity) then move it!
I'm Not an engineer, but I play one on TV. My handle is Tweety but I have nothing to do with the organization of similar name. I just had a really big head as a child so folks called me tweety bird.