I have to agree that DVD-Audio and SACD tend not to be very sensibly mixed. The way they ought to work is to give you a nice 3-channel soundstage across the front while the rear speakers just fill in the acoustics of the concert hall. Instead they tend to put the listener in the middle of the orchestra, which is just silly.
Having said that, the real advantage high-definition audio formats ought to have is one of sound quality rather than number of channels. Something that's 24-bit and 192kHz ought to sound far better than something that's 16-bit and 44.1kHz. But too many high-def recordings seem to be far more interested in the number of channels than they are in the quality of the recording.