I was just wondering if Akatosh put the 8 jewels (signifying the divines) around it to foretell of his ascendance? I couldn't find anything when I did a forum search.
The Ninth Gem (The Amulet itself) symbolizes the union of Human with Divine; it's the Red Diamond.
The Eight gems signify the Eight Divines, the Ninth Gem symbolizes the Covenant, aka, the Red Diamond itself symbolizes the Dragonborn, hence why only a Dragonborn; one with Divine (Dragon) blood but a mortal body, can wear it.