Well 7 is reserved for X so if you just added the following to /etc/inittab why not just reboot or didn't it work? You can also try the command init q
8:23:respawn:/sbin/getty 38400 tty8
9:23:respawn:/sbin/getty 38400 tty9
10:23:respawn:/sbin/getty 38400 tty10
11:23:respawn:/sbin/getty 38400 tty11
12:23:respawn:/sbin/getty 38400 tty12

BTW, if you add 13-24 you can get to them with right-Alt+Fn.