I didn't say anything about playing back two channels at once. Trick play is the ability to pause and rewind live tv. However, you have to switch back and fourth between the tuners to do so. You cannot have two images (one from each tuner) on your TV at once.

i.e. You can pause the channel you're watching and switch to another channel on the other tuner. Then, when you switch back to your first tuner, it will still be paused where you left it.

At no time during this process is the unit decoding more than one signal. Yes, it is recording the unwatched tuner in the background but it is not decoding it.