The best "official link" I've seen is this one from Sony and the general discription of the ITU 5.1 setup by Dr.AIX on AA. Though both are a far cry from any "detailed" setup that you are looking for.
http://www.sonymusic.com/sacd/faqdirect.html
http://db.audioasylum.com/cgi/m.pl?forum=hirez&n=79452&highlight=itu&r=&session=
http://www.sonymusic.com/sacd/faqdirect.html
http://db.audioasylum.com/cgi/m.pl?forum=hirez&n=79452&highlight=itu&r=&session=