SACD and DVD Audio are for high resolution music. I love DVD Audio and am waiting to have enough extra cash for a Denon 2200 to be able to finally play SACD. They are both excellent formats and worth the investment if you love music. The sound quality is usually much better than CD or vinyl, while also often being in full 5.1 sound as well as stereo.
Also I do not know about the Pioneer and Yamaha recievers, but Denon has an excellent feature called 5/6/7 channel stereo that turns stereo music which would normally only come out of the front two speakers and adds the other speakers making the same noise as the front. It is a similar effect to having front speakers and rear speakers in a car. It is an excellent feature for when you are hanging out with friends playing pool and want room filling sound beyond the limitations of Stereo.
