Kumihimo with 8 strands is just as simpel as with 4 strands, it is only an expansion on the basic Kumihimo.
Look at the scheme how to put the strand on to the kumihimo disc.
Then look at the schemes to make the pattern, repeat scheme 1 and 2 untill the cord is the size you wanted.
Scheme 1
Scheme 2
More patterns and ideas you can find in the book KUMIHIMO by Yoarra (dutch language)