With the insignia converter box you can manually set channels without scanning for them, then use the signal meter to try and tune it in. It even has an audio tone designating better/worse signal. Is this what you're talking about?
I have Westinghouse 32W6 and I can add channel by going to menu- find channel and enter the channel number related to frequency(not DTV channel number), it will scan and add the specific channels. I do not have to do a complete scan.Does anyone know of a DTV brand or model that will let you select a channel to search for rather than having to rescan?