I'll try to guide you the maze of these formats with both the geek explanations and my own simple-minded vocab. Damnit Jim...I'm only a writer not some kind of techno- whiz...
What is SACD?
Super Audio CD is a new format developed by Sony and Philips. It uses DSD (Direct stream digital) recording technology and a 4.7GB disc to give the consumer an audio experience so real you think you are in the recording studio or front row at a concert. ....or in the middle of the orchestra pit. Says me....as the anagram suggests, SACD is designed to play on your cd players. SACD discs come in 3 different formats. A single layer SACD will play on an SACD compatible player only. Dual layer SACDs can hold almost double the information as a single layer SACD.
In other words; those double cds in your collection can be transferred to one dual-layered SACD. Like the single layer SACD, dual-layered SACDs will only play on an SACD compatible cd player. And finally, the hybrid SACD has a single high density layer and a cd layer. These SACDs will play on your fancy SACD player in the livingroom, in your car stereo and on that crappy cd player on your bedside table. Important to note: SACD compatible players will play any type of cd available. SACDs can come in multichannel or stereo variants. Some titles, like Jeff Beck's "Blow by Blow" are offered in either a stereo version or a multichannel version. Other artists with SACD releases include Stevie Ray Vaughan, Aerosmith, and Pink Floyd and hundreds(!) of others.