Probably the biggest debate in the Surround recording industry is how to handle bass. Since 5.1 Surround has a subwoofer, you have the option of leaving bass in the 5 full-range channels or moving all the lower bass to the subwoofer, or a blend of both.
The design of consumer decoders seems to be driving the direction of bass management. Most consumer decoders have a cross-over in each of the 5 full-range channels to remove the bass below a certain frequency and send it to the subwoofer, to be added to whatever bass is already recorded into the subbass channel (called the LFE channel, for "low frequency enhancement"). Some consumer decoders allow you to select the crossover by frequency, and others allow you to select "large speakers" or "small speakers" to allow the unit to guess the low-frequency capabilities of your 5 full-range speakers. In short, most recording engineers send at least some bass to the 5 full-range channels, and allow the decoder to redirect it to the subwoofer based on the individual home setup.
The LFE channel gets a +10dB gain on playback. This gives you the option of delivering some really powerful deep bass during playback, such as in that earthquake sound effect in your recording. Consider also that this +10 dB of low bass can also be added to any low bass that came out of the other 5 channels, so you realistically can deliver a sound from the subwoofer that is more than +20dB above the sound from any other speaker.
What this means during recording is that your studio has to have the analog gain to the subwoofer set to +10 dB relative to the other 5 speakers, so that you will hear the sound as it will be played back in the home theater systems, and you will get your levels set right in the mix.
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