Correct. You do not need to turn on the HT pre-amp/amp/receiver if you are listening to 2 channel audio and have a source component connected to the 2-channel portion of the rig. You would only need to turn on the HT electronics when you are listening to a multi-channel source played through the HT rig. You would also need to have the 2-channel setup powered up for multi-channel too, as it powers the front L&R speakers in the system I describe.
Good luck, and enjoy.....