I just received the following answer from Western Digital Customer Service and Support:
By reading your email,i understand that you would like to know whether you may use different internal hard drives than Green ones for your My Book Studio Edition II.
I would like to inform you that the product in question is a legacy product (EOL=end of life) thus an old one and most likely will eject other hard drive models and/or higher capacity drives. We have never tested it anyway.
The below is a typical message you would see in such case:
‘‘The slot contains an HDD that does not meet the unit’s requirements.Install a drive that is compatible with RAID device.’’
Under this aspect,only WD Green Drives are compatible. If you are unable to find any green drives around online (or not),then we do recommend purchasing a newer model.
If you have any further questions, please reply to this email and we will be happy to assist you further.
Unfortunately, it seems that this product cannot be used any more.
Thanks for your support!