My 522 is "Modded" so it's a little different, but the concepts are still the same. basically what's going on is the diplexer allows power to pass from the receiver and power the LNB also has a band pass filter on one port that disallows any frequency above 700 Mhz sometimes 330 Mhz depending so when you mix them back together you shouldn't get overlap or interference, You said you have comcast internet before, you don't wan't to diplex the satellite into the cable, It can cause all kinds of problems, it may work if everything is just right but generally it just Fu(ks everything up.