Eternal Sonata is working in multiMAN v1.15; insert a BD-Game(any game) on the drive and choose the game with [Select+X] combination button.
After that it will ask you a message that it will mount something... Choose Yes on the selection and it will return you to XMB.
Once on XMB, Choose the BD-Game.. which is named as Eternal Sonata on the BD-game.
There the game boots... works fine on my side.
Model: CECHC04 PAL/EUR 60GB SKU Console
Firmware: REBUG 3.55 CFW [DEBUG MODE, DEBUG XMB, MENU OPTION 2]
BM: Iris Manager v1.2 (Hermes Syscall8)