First off, I posted that last response to suggest I found it slightly hard to believe he truly had only 7 abdominals because it would be fairly obvious. Look at the picture again and you'll see the RAs have 8 definitive divisions. In every case I have seen, pretty much without fail, the amount of work required to get the lower abdominals to clearly show their division is an uphill battles against genetics.
Here are a couple body builders. You'll notice the top center BB has asymmetrical abs which is fairly common (from my experience). You'll also notice not a one of them has the division you're talking about. These are insanely well developed men with extremely low bf%. The reason behind this is probably because of their training and the kinds of hypertrophy they experience, but I'm using this to show not everyone can get an 8 pack and even amongst body builders you'll see asymmetrical balances.
On to your specific question:
One how do you get an eight pack when you have only 6 easily identifiable muscles which are commonly associated with abs?
You just answered your own question. "Easily identifiable" is the key word here.
Here is a picture from the bodybuilding forums.
To get this you need to lose fat in a place where a vast majority of men genetically store body fat. Your body is seriously reluctant to lose fat. So getting these to show is a fight against genetics.
I still would like to see a pic so I know what exactly he's referring to.