I don't believe ATA66/ATA100 will make any difference to the empeg. I remember reading (but cannot find the post) that the empeg uses an ATA/33 controller. Since the HD cable is a 40 wire not an 80 wire, the controller must be 66 or 33. An ATA/100 drive will work at the slower speeds. Since the price is the same, I don't think it matters which one you get.

-Zeke