[QUOTE=Goit;2061357]If the DVD and SACD are all 5.1, what is the use of 6.1 or 7.1?[/QUOTE]
On a PC, almost none except for games.
In a HT setup, it offers greater depth of the sound field when used with decoders like DD-EX, DTS-ES, DD PLIIx and of course the lossless HD audio codecs. Most AVRs also offer 7:1 sound field processing.