The LFE channel should never be mixed into the mains when a receiver is set to no subwoofer. That's a decree from Dolby, and from what I understand it is followed by everyone.
That doesn't mean that the main channels can't have their own < 100 Hz content that will still get played. The LFE channel is designed to contain effects, like textured rumbles. While the main channels contain content sensitive information, like the sound of an explosion.
Because of this recommendation bass notes of music, no matter how low, should never be mixed on the LFE channel, because with no sub, the notes would not be heard.
