The SACD format's design allows for audio data from 1 Hz to 100,000 Hz. DVD-Audio tops out at 48,000 Hz. Most electronics are designed with the <20,000 Hz range of human hearing, although there are some "super-tweeters" on the market that are capable of reproducing audio up as high as 40,000 Hz. Denon's giving folks the option of discarding the audio data that's beyond even the reach of those rarely-used drivers, leaving you with something comparable to DVD-Audio as far as frequency response. And since some purists may want to get the full, un-altered frequency response from SACD, they give you the option of disabling it and letting the full 1 to 100,000Hz through.