You can also take midnight bus. It will take 8.5 hours and 6,200 JPY.
◆両備高速バス◆岡山⇔名古屋(両備バス)両備バス
Sorry,they have no English page. Ask them via phone or e-mail.
086-232-6688 (from inside Japan) or
+81-86-232-6688(from outside Japan)
kousoku@ryobi-holdings.jp