The STK600 uses a combination of routing and socket cards to let all AVR devices to be mounted. Given the device, only certain combinations of routing and socket cards are valid. The Card stack page has information about this.
Figure 1. Card Stack
The card stack page tells which cards are mounted on the STK600 and if they support the selected device. If they do match, a list of devices supported by that card combination is listed.
If the mounted cards do not match, a list of suggested card combinations will be listed.