There is only 1 OTA tuner, you can watch one OTA channel and you can record it at the same time. You can watch a satellite channel though while recording an OTA channel. If you want to record one OTA and watch a different OTA one, you will have to use the 921 to record then tune your TV to the other channel.
If you need more OTA channel recording, connect your OTA anrtenna for the 8VSB tuner and then also sub to the Dish locals. Now you can record both OTA stations at the same time but unfortunately, only the OTA antenna will get you HD as the Dish LIL is not doing local HDTV channels.