I know that it is 76-key, has the sound engine of the xv-5080, and is a good workstation, but doesn't have sampling. It is expandable through JV-SR and SRX cards (two each). It also has a nice big scrren so it's a bit easier to navigate and edit sounds/parameters. The major difference between it and the later fantoms is lack of sampling capability and different sound engine. But, I heard that it sounds wonderful. Also, $550 is a decent price, considering that they retailed for way more than that, and the current used value on ebay is about that much, sometimes a little more. I hope that helps!
p_music