Enter channel number 94.1 (WVLA cable box channel 703). Then try entering channel number 33.1. One or both should get you your local "HD" version of your local NBC station.
Enter channel number 100.4 (WAFB cable box channel 707). Then try entering channel number 100.4. One or both should get you your local "HD" version of your local CBS station.
FWIW, without any cable connected to the Mag, for the hell of it, I was able to at least enter 94.1 and it appeared to stay on that channel, at least according to the front display. It will be about another hour before I can hook cable back up to it.