Problems reading backup CD on Xbox

[TAAG75]

I've a Xbox modified with Enigmah chip,
If I try to read any copied CD (audio CD and Burnt iso files on CD), Xbox doesn't recognize the CDs. I've tried different type of them, but nothing. Do I need to use special CD, can you suggest me some of them? The only ones that I can read are those audio CD made in Hong Kong, but they aren't made by burning process.
Thank you very much.