CONFIG_EMBEDDED6xx is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Embedded 6xx/7xx/7xxx-based boards

configname: CONFIG_EMBEDDED6xx

Linux Kernel Configuration
└─>Embedded 6xx/7xx/7xxx-based boards
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
depends
CONFIG_6xx
CONFIG_BROKEN_ON_SMP

is selected by
CONFIG_GAMECUBE
CONFIG_WII