Dak, the sub out on a receiver/processor usually is derived from two sources: the bass frequencies from any speaker channels set "small"(typically below 80Hz); the LFE(low frequency effects)occasionally present in the .1 channel in 5.1 or higher movie source material. This is all low-passed to the sub.
I'd like to try to answer more fully, but I'm puzzled by a couple points: what is the feature of your processor that somehow relates turning off the subwoofer to the frequency range in the regular L/R outputs? Also, I don't follow what you mean in the "L/R 600" vs "dedicated EP-800" sentence.
