The Defeat button turns off the EQ (whichever one your using), MX, bass compensation, etc... but not the x-over in order to protect the speakers. Any time you use the EQ you want to make sure the Defeat button is turned off. It's nice in that you can hear the differences between a flat EQ and the changes you've made by switching back and forth. If you have the H700 then try not to use the MX or bass compensation as they tend to muddy the bass and change all kinds of things.
That first list is the correction numbers for the digital Radio Shack meter. Anything under 20Hz should probably be blocked anyway. There's pretty much no music down there unless you listen to specially recorded albums that have cannon blasts or pipe organs. They can play that low, but you will also need the subs and the power to reproduce them otherwise you'll just damage your equipment. In fact, the H700 has a high pass filter on the subs that you can set to 20Hz and a 30dB slope to act as a subsonic filter.
Anything below 20Hz is considered subsonic and usually below the threshold of human hearing. You will feel it though, like an earthquake, but you won't hear anything. Usually subsonics will cause your woofers to flap around wildly.
I want to write up a philosophy for EQ tuning as well. I just don't have time right this minute. Basically do as much sound shaping as you can with speaker positioning and crossovers so that you have the smallest amount of correction as possible with the EQ.
The EQ is sort of the last resort and needs to be as little as possible.
Always reduce the peaks in your cars response first as they will be the most noticable to your ears.
It's always preferable to cut a freq than it is to boost a freq. becausing boost will add some distortion.
I'll try to add more in the next few days.
If anyone does use the Radio shack digital meter and plot their cars response, post it up here so I can see it. I'll point out the areas that need attention. We'll try the x-overs first as well as the amp gains to get the sound balanced as much as possible before seeing what EQ corrections need to be made. You want to shoot for no more than about 4dB of correction on any particular freq. It all depends though. Just don't overcorrect. Most view the EQ as a crutch, but it can really make the difference between so-so sound and really spectacular sound, especially in a car setup. Cars are just ugly beasts to a sound system. No doubt about that.