You must enable the digital audio option to hear audio from an emulated image.
ON Win98/Me:
Go to Control Panel=>Multimedia=>CD audio=>select the CDROM drive letter=>tick Enable digital CD audio for this CD-ROM device;
ON Win2K/XP:
Go to My Computer=>Right Click CDROM's ICon=>Properties=>harware=>ZTekWare Original CD Emulator=>Properties=>tick Enable digital CD audio for this CD-ROM device;